Add ad-free YouTube player built on zero-native

Desktop YouTube player with no login and no ads. Extracts direct
video/audio streams with yt-dlp and plays them in a native window via
zero-native (Zig + system WebView) for a tiny footprint vs Electron.

- Dual-stream engine: muted video synced with separate audio track for
  high quality without ffmpeg muxing; progressive fallback
- On-device playlists, watch history, audio-only mode
- Full custom controls: seek, volume, speed, quality, fullscreen, queue
- Zig bridge handlers spawn yt-dlp and return slimmed JSON to the web UI
- Cinematic dark UI: Bricolage/Hanken/JetBrains Mono, vermilion accent

.gitignore

@@ -0,0 +1,20 @@
+# yt-dlp binary is downloaded by scripts/setup-ytdlp.js
+bin/yt-dlp
+bin/yt-dlp.exe
+
+# zero-native / zig build artifacts
+zig-out/
+.zig-cache/
+zig-cache/
+
+# generated scaffold (regenerate with `zero-native init`)
+build.zig
+build.zig.zon
+src/runner.zig
+
+# node
+node_modules/
+
+# local data
+*.tmp
+.DS_Store