feat(renderer): video player with HLS.js & YouTube embed (M10.12)

- VideoPlayer.vue: native <video> with custom glass styling
- HLS.js lazy-loaded for adaptive streaming (.m3u8)
- YouTube detection → youtube-nocookie.com embed
- Fullscreen via native controls, playsinline for mobile

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

packages/app/package.json

@@ -21,6 +21,7 @@
   "dependencies": {
     "@aiui/core": "workspace:*",
     "@tanstack/vue-virtual": "^3.13.19",
+    "hls.js": "^1.6.15",
     "katex": "^0.16.33",
     "leaflet": "^1.9.4",
     "markdown-it": "^14.1.1",