tb-scripts: add .sh extensions and add ,yt-dlp wrapper

Rename all shell script files to use .sh extensions for consistency
and better editor support (pushover-send, split-1G, xz, zipdir).
Update default.nix references to match the new filenames.

Add a new ,yt-dlp script that runs yt-dlp from nixpkgs-unstable
via `nix run`, so it's always up to date without needing to be
in the system packages.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pkgs/tb-scripts/pushover-send.sh

@@ -0,0 +1,47 @@
+#!/usr/bin/env bash
+# Send a pushover notification.
+# Usage: pushover-send [--pid <pid>] [message]
+#   --pid <pid>  Wait for process to finish before sending
+#   message      Optional message (default: "Job done.")
+
+pid=""
+message=""
+
+# Parse arguments
+while [[ $# -gt 0 ]]; do
+  case "$1" in
+    --pid)
+      pid="$2"
+      shift 2
+      ;;
+    *)
+      message="$1"
+      shift
+      ;;
+  esac
+done
+
+# Default message
+if [ -z "$message" ]; then
+  message="Job done."
+fi
+
+# Wait for PID if specified
+if [ -n "$pid" ]; then
+  if ! [[ "$pid" =~ ^[0-9]+$ ]]; then
+    echo "Error: PID must be a number" >&2
+    exit 1
+  fi
+  if [ ! -d "/proc/$pid" ]; then
+    echo "Error: Process $pid does not exist" >&2
+    exit 1
+  fi
+  tail --pid="$pid" -f /dev/null 2>/dev/null
+fi
+
+curl \
+    https://api.pushover.net/1/messages.json \
+    --data-urlencode "token=ak8z7cbxim2t7eksvj7dtudo6cdxgj" \
+    --data-urlencode "user=u8hjgdf1hquocmy682w9xfmpf3479u" \
+    --data-urlencode "priority=1" \
+    --data-urlencode "message=$message"