home/develop/emacs: add yasnippet snippets and make snippet dirs configurable

This commit makes two significant changes to the Emacs configuration:

1. Refactors emacs.nix to use proper NixOS module structure:
   - Converts from simple configuration to a module with options/config
   - Adds `tb.emacs.extraSnippetDirs` option to allow per-machine snippet
     directories (defaults to ~/.emacs.d/snippets/)
   - Moves yasnippet configuration from custom.el to nix-generated elisp,
     enabling dynamic snippet directory configuration via Nix

2. Adds a comprehensive collection of yasnippet snippets for multiple modes:
   - C++ mode: 50 snippets for common patterns (class, namespace, operators,
     copy/move semantics, debug helpers, documentation, threading primitives)
   - CC mode (shared C/C++): for, switch, main, include guards, etc.
   - CMake mode: if/else, foreach, function, macro, project boilerplate
   - LaTeX mode: document structure, beamer frames, figures, lists
   - Perl mode: package boilerplate, shebang
   - Python/Shell/Nix/Protobuf/Java/CSS/Dockerfile modes: horizontal rules
     and common patterns
   - Text mode: modeline snippets for locale settings

The snippets use yasnippet's inheritance system via .yas-parents files,
so c++-mode inherits from cc-mode and text-mode, reducing duplication.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

home/develop/emacs/snippets/c++-mode/.yas-parents

@@ -0,0 +1,2 @@
+cc-mode
+text-mode

home/develop/emacs/snippets/c++-mode/A

@@ -0,0 +1,6 @@
+# -*- mode: snippet; require-final-newline: nil -*-
+# name: A
+# key: A
+# binding: direct-keybinding
+# --
+ASSERT_EQ($0)

home/develop/emacs/snippets/c++-mode/acc

@@ -0,0 +1,5 @@
+# -*- mode: snippet -*-
+# name: ac
+# key: ac
+# --
+*  @param[in] alloc Memory allocator to use.

home/develop/emacs/snippets/c++-mode/alloc

@@ -0,0 +1,5 @@
+# -*- mode: snippet -*-
+# name: alloc
+# key: alloc
+# --
+const xplat::polymorphic_allocator<> alloc;

home/develop/emacs/snippets/c++-mode/ator

@@ -0,0 +1,5 @@
+# -*- mode: snippet -*-
+# name: ator
+# key: ator
+# --
+const xplat::polymorphic_allocator<> alloc;

home/develop/emacs/snippets/c++-mode/be

@@ -0,0 +1,5 @@
+# -*- mode: snippet -*-
+# name: be
+# key: be
+# --
+$1.begin(), $1.end()

home/develop/emacs/snippets/c++-mode/cerr

@@ -0,0 +1,8 @@
+# -*- mode: snippet -*-
+# contributor: York Zhao <gtdplatform@gmail.com>
+# name: cerr
+# key: cerr
+# --
+`(progn (save-excursion) (goto-char (point-min)) (unless (re-search-forward
+"^using\\s-+namespace std;" nil 'no-errer) "std::"))
+`cerr << $0 << '\n';

home/develop/emacs/snippets/c++-mode/class

@@ -0,0 +1,13 @@
+# -*- mode: snippet; require-final-newline: nil -*-
+# name: class
+# key: class
+# binding: direct-keybinding
+# --
+class ${1:Class}
+{
+public:
+    $1()
+        : { }
+
+private:
+};

home/develop/emacs/snippets/c++-mode/cmd

@@ -0,0 +1,10 @@
+# -*- mode: snippet -*-
+# name: cmd
+# key: cmd
+# --
+static void ${1:cmd}(base::Cmd& cmd)
+{
+    $0
+}
+
+CMD($1, "$1");

home/develop/emacs/snippets/c++-mode/constructor

@@ -0,0 +1,8 @@
+# -*- mode: snippet -*-
+# name: constructor
+# key: ct
+# --
+${1:Class}::$1(${2:args}) ${3: : ${4:init}}
+{
+        $0
+}

home/develop/emacs/snippets/c++-mode/copy

@@ -0,0 +1,6 @@
+# -*- mode: snippet; require-final-newline: nil -*-
+# name: copy
+# key: copy
+# binding: direct-keybinding
+# --
+ * Copyright (C) `(format-time-string "%Y" (current-time))` Timo Bingmann <tb@panthema.net>

home/develop/emacs/snippets/c++-mode/copymove

@@ -0,0 +1,14 @@
+# -*- mode: snippet; require-final-newline: nil -*-
+# name: copymove
+# key: copymove
+# binding: direct-keybinding
+# expand-env: ((yas-indent-line 'fixed))
+# --
+//! default copy-constructor
+${1:class}(const $1 &) = default;
+//! default assignment operator
+$1 & operator = (const $1 &) = default;
+//! move-constructor: default
+$1($1 &&) = default;
+//! move-assignment operator: default
+$1 & operator = ($1 &&) = default;

home/develop/emacs/snippets/c++-mode/cout

@@ -0,0 +1,8 @@
+# -*- mode: snippet -*-
+# contributor: York Zhao <gtdplatform@gmail.com>
+# name: cout
+# key: cout
+# --
+`(progn (save-excursion) (goto-char (point-min)) (unless (re-search-forward
+"^using\\s-+namespace std;" nil 'no-errer) "std::"))
+`cout << $0 << '\n';

home/develop/emacs/snippets/c++-mode/cv

@@ -0,0 +1,5 @@
+# -*- mode: snippet -*-
+# name: cv
+# key: cv
+# --
+std::cout << "$1 " << $1 << std::endl;

home/develop/emacs/snippets/c++-mode/d

@@ -0,0 +1,5 @@
+# -*- mode: snippet -*-
+# name: d
+# key: d    
+# --
+qDebug() << 

home/develop/emacs/snippets/c++-mode/debug

@@ -0,0 +1,6 @@
+# -*- mode: snippet; require-final-newline: nil -*-
+# name: debug
+# key: debug
+# binding: direct-keybinding
+# --
+static constexpr bool debug = true;

home/develop/emacs/snippets/c++-mode/debugf

@@ -0,0 +1,6 @@
+# -*- mode: snippet; require-final-newline: nil -*-
+# name: debugf
+# key: debugf
+# binding: direct-keybinding
+# --
+static constexpr bool debug = false;

home/develop/emacs/snippets/c++-mode/doc

@@ -0,0 +1,7 @@
+# -*- mode: snippet -*-
+# name: doc
+# key: doc
+# --
+/**
+ * @brief $1
+ */

home/develop/emacs/snippets/c++-mode/dog

@@ -0,0 +1,12 @@
+# -*- mode: snippet; require-final-newline: nil -*-
+# name: dog
+# key: dog
+# binding: direct-keybinding
+# expand-env: ((yas-indent-line 'fixed))
+# --
+//! \\name $1
+//! \\{
+
+$0
+
+//! \\}

home/develop/emacs/snippets/c++-mode/el

@@ -0,0 +1,5 @@
+# -*- mode: snippet -*-
+# name: el
+# key: el
+# --
+ << std::endl

home/develop/emacs/snippets/c++-mode/functor

@@ -0,0 +1,14 @@
+# -*- mode: snippet -*-
+# name: functor
+# key: functor
+# --
+class ${1:Functor}
+{
+public:
+    $1($2) { }
+
+    void operator () () const {
+    }
+
+private:
+};

home/develop/emacs/snippets/c++-mode/hi

@@ -0,0 +1,5 @@
+# -*- mode: snippet -*-
+# name: hi
+# key: hi
+# --
+/*`(make-string (- 78 (current-column)) ?-)`*/

home/develop/emacs/snippets/c++-mode/i

@@ -0,0 +1,6 @@
+# -*- mode: snippet; require-final-newline: nil -*-
+# name: i
+# key: i
+# binding: direct-keybinding
+# --
+`(if (char-equal ?) (preceding-char)) "," "")` m_${1:var}($1)

home/develop/emacs/snippets/c++-mode/lock

@@ -0,0 +1,6 @@
+# -*- mode: snippet; require-final-newline: nil -*-
+# name: lock
+# key: lock
+# binding: direct-keybinding
+# --
+std::unique_lock<std::mutex> lock$1(mutex$1_);

home/develop/emacs/snippets/c++-mode/mutexlock

@@ -0,0 +1,7 @@
+# -*- mode: snippet; require-final-newline: nil -*-
+# name: mutexlock
+# key: mutexlock
+# binding: direct-keybinding
+# --
+static std::mutex mutex$1;
+std::unique_lock<std::mutex> lock$1(mutex$1);

home/develop/emacs/snippets/c++-mode/mysource

@@ -0,0 +1,17 @@
+# -*- mode: snippet; require-final-newline: nil -*-
+# name: mysource
+# key: mysource
+# binding: direct-keybinding
+# --
+/*******************************************************************************
+ * $1/<file>
+ *
+ * $2
+ ******************************************************************************/
+
+namespace $1 {
+
+
+} // namespace $1
+
+/******************************************************************************/

home/develop/emacs/snippets/c++-mode/nl

@@ -0,0 +1,5 @@
+# -*- mode: snippet -*-
+# name: nl
+# key: nl
+# --
+// NOLINTNEXTLINE($1)

home/develop/emacs/snippets/c++-mode/noncopy

@@ -0,0 +1,10 @@
+# -*- mode: snippet; require-final-newline: nil -*-
+# name: noncopy
+# key: noncopy
+# binding: direct-keybinding
+# expand-env: ((yas-indent-line 'fixed))
+# --
+//! non-copyable: delete copy-constructor
+${1:class}(const $1 &) = delete;
+//! non-copyable: delete assignment operator
+$1 & operator = (const $1 &) = delete;

home/develop/emacs/snippets/c++-mode/noncopymove

@@ -0,0 +1,14 @@
+# -*- mode: snippet; require-final-newline: nil -*-
+# name: noncopymove
+# key: noncopymove
+# binding: direct-keybinding
+# expand-env: ((yas-indent-line 'fixed))
+# --
+//! non-copyable: delete copy-constructor
+${1:class}(const $1 &) = delete;
+//! non-copyable: delete assignment operator
+$1 & operator = (const $1 &) = delete;
+//! move-constructor: default
+$1($1 &&) noexcept = default;
+//! move-assignment operator: default
+$1 & operator = ($1 &&) noexcept = default;

home/develop/emacs/snippets/c++-mode/ns

@@ -0,0 +1,10 @@
+# -*- mode: snippet; require-final-newline: nil -*-
+# name: namespace
+# key: ns
+# binding: direct-keybinding
+# --
+namespace $1 {
+
+$0
+
+} // namespace $1

home/develop/emacs/snippets/c++-mode/operator_equal

@@ -0,0 +1,5 @@
+# -*- mode: snippet -*-
+# name: al
+# key: al
+# --
+allocator_type alloc

home/develop/emacs/snippets/c++-mode/operator_istream

@@ -0,0 +1,8 @@
+# -*- mode: snippet -*-
+# name: operator>>
+# key: op>>
+# --
+istream& operator>>(istream& s, const ${1:type}& ${2:c})
+{
+         $0
+}

home/develop/emacs/snippets/c++-mode/operator_less

@@ -0,0 +1,8 @@
+# -*- mode: snippet -*-
+# name: operator<
+# key: op<
+# --
+friend bool operator < (const ${1:type}& a, const $1& b)
+{
+         return $0;
+}

home/develop/emacs/snippets/c++-mode/operator_ostream

@@ -0,0 +1,8 @@
+# -*- mode: snippet -*-
+# name: operator<<
+# key: op<<
+# --
+friend std::ostream& operator << (std::ostream& os, const ${1:type}& ${2:x})
+{
+         return os << $0;
+}

home/develop/emacs/snippets/c++-mode/os

@@ -0,0 +1,5 @@
+# -*- mode: snippet -*-
+# name: os
+# key: os
+# --
+os << " $1=" << x.$1;

home/develop/emacs/snippets/c++-mode/oso

@@ -0,0 +1,6 @@
+# -*- mode: snippet -*-
+# name: oso
+# key: oso
+# --
+if (${2:t}.${1:var})
+    os << " $1=" << $2.$1;

home/develop/emacs/snippets/c++-mode/oss

@@ -0,0 +1,6 @@
+# -*- mode: snippet -*-
+# name: oss
+# key: oss
+# --
+std::ostringstream oss;
+oss << $0

home/develop/emacs/snippets/c++-mode/pe

@@ -0,0 +1,5 @@
+# -*- mode: snippet -*-
+# name: pe
+# key: pe
+# --
+v.$1 += p.$1;

home/develop/emacs/snippets/c++-mode/perl

@@ -0,0 +1,8 @@
+# -*- mode: snippet -*-
+# name: perl
+# key: perl
+# --
+/*[[[perl
+  $0
+ ]]]*/
+//[[[end]]]

home/develop/emacs/snippets/c++-mode/q

@@ -0,0 +1,10 @@
+# -*- mode: snippet -*-
+# name: q
+# key: q
+# --
+db::Query q = cmd.db_.query << "SELECT $1"
+                            << into(...);
+
+while (q.next())
+{
+}

home/develop/emacs/snippets/c++-mode/stdrand

@@ -0,0 +1,6 @@
+# -*- mode: snippet; require-final-newline: nil -*-
+# name: stdrand
+# key: stdrand
+# binding: direct-keybinding
+# --
+std::default_random_engine ${1:name}(std::random_device { } ())

home/develop/emacs/snippets/c++-mode/stdsleep

@@ -0,0 +1,6 @@
+# -*- mode: snippet; require-final-newline: nil -*-
+# name: stdsleep
+# key: stdsleep
+# binding: direct-keybinding
+# --
+std::this_thread::sleep_for(std::chrono::seconds($1));

home/develop/emacs/snippets/c++-mode/sv

@@ -0,0 +1,5 @@
+# -*- mode: snippet -*-
+# name: sv
+# key: sv
+# --
+std::string_view

home/develop/emacs/snippets/c++-mode/svlit

@@ -0,0 +1,5 @@
+# -*- mode: snippet -*-
+# name: svlit
+# key: svlit
+# --
+using namespace std::string_view_literals;

home/develop/emacs/snippets/c++-mode/timestamp

@@ -0,0 +1,9 @@
+# -*- mode: snippet -*-
+# name: timestamp
+# key: timestamp
+# --
+//! Time is measured using chrono::steady_clock
+static double timestamp() {
+    return std::chrono::duration_cast<std::chrono::duration<double> >(
+        std::chrono::steady_clock::now().time_since_epoch()).count();
+}

home/develop/emacs/snippets/c++-mode/try

@@ -0,0 +1,10 @@
+# -*- mode: snippet -*-
+# name: try
+# key: try
+# a bit too intrusive now still, not always I want to do this
+# --
+try {
+    $0
+} catch (${1:std::exception& e}) {
+
+}

home/develop/emacs/snippets/c++-mode/using_ator

@@ -0,0 +1,5 @@
+# -*- mode: snippet -*-
+# name: using_ator
+# key: using
+# --
+using allocator_type = xplat::polymorphic_allocator<>;

home/develop/emacs/snippets/c++-mode/vls

@@ -0,0 +1,5 @@
+# -*- mode: snippet -*-
+# name: ls
+# key: ls
+# --
+common::allocate_local_shared