Add custom script packages with Nix dependency management

This commit introduces two new custom script packages: tb-scripts for
all systems and tb-dev-scripts for development machines. These packages
provide a maintainable way to distribute utility scripts across the
infrastructure with proper dependency management.

Created pkgs/ directory with two script collections:

1. **tb-scripts** - General utilities available on all systems:
   - ,jq_reformat: Reformat JSON files in-place with atomic file operations
   - ,rename_lower: Convert filenames to lowercase with validation

2. **tb-dev-scripts** - Development-specific tools:
   - ,cmake_update_fetchcontent: Update CMake FetchContent dependencies

All scripts have been significantly enhanced from their original versions:

- Proper quoting to handle filenames with spaces
- Secure temporary file creation using mktemp
- Atomic file replacement to prevent data loss
- Input validation and comprehensive error handling
- Usage help with -h/--help flag
- Extensive inline comments explaining each section
- Cleanup traps on error

- Complete rewrite in Python for consistency
- Validates files exist before attempting rename
- Checks if target lowercase filename already exists
- Skips files already lowercase (no-op)
- Descriptive error messages for each failure case
- Usage documentation with examples
- Proper exit codes

- Interactive CMake FetchContent dependency updater
- Recursively finds all CMakeLists.txt files via add_subdirectory()
- Queries GitHub API for latest releases/tags
- Compares semantic versions and commit hashes
- Shows available updates in formatted table
- Prompts for confirmation before applying updates
- Atomic file updates with validation

Scripts are packaged using writeShellApplication with proper dependency
injection via runtimeInputs:

- tb-scripts requires: jq, python3
- tb-dev-scripts requires: python3, git

Dependencies are automatically available in PATH when scripts run,
eliminating manual dependency checks.

Created system module files to import the script packages:

- system/default/scripts.nix: Adds tb-scripts to nixosModules.default
- system/develop/scripts.nix: Adds tb-dev-scripts to nixosModules.develop

Updated flake.nix to import these modules in the appropriate contexts.

- Scripts have proper Nix-managed dependencies
- No manual installation or PATH configuration needed
- Easy to extend with additional scripts
- Scripts are validated with shellcheck during build
- Clear separation between all-systems and dev-only utilities
- Comprehensive error handling and user documentation

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

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

pkgs/tb-dev-scripts/default.nix

@@ -0,0 +1,20 @@
+{ pkgs }:
+
+pkgs.symlinkJoin {
+  name = "tb-dev-scripts";
+  meta = {
+    description = "Custom development scripts for TB";
+    maintainers = [ ];
+  };
+  paths = [
+    (pkgs.writeShellApplication {
+      name = ",cmake_update_fetchcontent";
+      runtimeInputs = [ pkgs.python3 pkgs.git ];
+      text = ''
+        python3 - "$@" <<'PYTHON_SCRIPT'
+        ${builtins.readFile ./cmake_update_fetchcontent.py}
+        PYTHON_SCRIPT
+      '';
+    })
+  ];
+}