Add yt-dlp "Download Video" Chromium extension

Download the current page's video with yt-dlp via Alt+Shift+D or a click
on the toolbar icon. A native-messaging host runs the download, shows live
progress on the Quickshell OSD, and posts a clickable "Download complete"
toast that opens the file in mpv.

- Extension: pinned key for a stable id, green download-video icon,
  keyboard command + toolbar action (reads the active tab URL).
- Native host (omarchy-chromium-ytdlp-host): verifies the URL with
  yt-dlp --simulate (else "No video found"), streams progress to the OSD
  (time-throttled to ~4/s), saves to ~/Videos, opens mpv on click.
- Installer (omarchy-install-chromium-ytdlp) writes the native-messaging
  manifest into installed Chromium/Chrome/Brave/Edge profiles; wired into
  browser install and chromium refresh, with a migration for existing users.
- omarchy-osd: add -d/--duration so the OSD can persist during a download.
- Add yt-dlp to base packages, load the extension via --load-extension,
  and document the Alt+Shift+D binding.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

migrations/1780517689.sh

@@ -0,0 +1,25 @@
+echo "Add yt-dlp download extension (Alt+Shift+D) to Chromium-based browsers"
+
+YTDLP_EXT="$OMARCHY_PATH/default/chromium/extensions/yt-dlp"
+
+add_ytdlp_extension() {
+  local file=$1
+
+  [[ -f $file ]] || return 0
+  grep -q "extensions/yt-dlp" "$file" && return 0
+
+  if grep -q "^--load-extension=" "$file"; then
+    sed -i --follow-symlinks "s|^--load-extension=\(.*\)$|--load-extension=\1,$YTDLP_EXT|" "$file"
+  else
+    echo "--load-extension=$YTDLP_EXT" >>"$file"
+  fi
+}
+
+for conf in chromium chrome google-chrome brave brave-beta brave-nightly brave-origin-beta microsoft-edge-stable; do
+  add_ytdlp_extension "$HOME/.config/$conf-flags.conf"
+done
+
+omarchy-pkg-add yt-dlp
+
+# Register the native messaging host that runs yt-dlp for the extension.
+omarchy-install-chromium-ytdlp || true