refactor: render external audio controls with React

Co-authored-by: OpenCode (gpt-5.6-sol) <noreply@opencode.ai>

Author: hi-ogawa

packages/youtube-external-audio/README.md

@@ -37,4 +37,4 @@ follows the resulting media events.
 
 The YouTube content-script integration patterns are adapted from
 [Zamak (ytsub-v5)](https://github.com/hi-ogawa/ytsub-v5), as documented next
-to the adapted lifecycle code in `src/content.ts`.
+to the adapted lifecycle code in `src/content.tsx`.

packages/youtube-external-audio/package.json

@@ -7,12 +7,19 @@
     "build": "vite build && cd dist/extension && zip -r ../extension.zip .",
     "typecheck": "tsc --noEmit",
     "lint": "pnpm typecheck",
-    "test": "vitest run",
+    "test": "vitest run src",
     "test-e2e": "playwright test"
   },
+  "dependencies": {
+    "react": "^19.2.3",
+    "react-dom": "^19.2.3"
+  },
   "devDependencies": {
     "@playwright/test": "^1.61.1",
     "@types/node": "^26.1.1",
+    "@types/react": "^19.2.14",
+    "@types/react-dom": "^19.2.3",
+    "@vitejs/plugin-react": "^6.0.3",
     "typescript": "^7.0.2",
     "vite": "^8.1.4",
     "vitest": "^4.1.10"