fix: bundle the content script to stop 'Unsafe attempt to load URL' errors

Dynamic import() of extension modules from a content script makes Chrome log
'Unsafe attempt to load URL chrome-extension://...' on YouTube pages, which fills
the extension's error list even though the modules load (HTTP 200). The content
script is now one classic file built by 'npm run build'; web_accessible_resources
is no longer needed and is removed.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

manifest.json

@@ -13,11 +13,5 @@
       "js": ["src/content.js"],
       "run_at": "document_idle"
     }
-  ],
-  "web_accessible_resources": [
-    {
-      "resources": ["src/lib/*.js"],
-      "matches": ["https://www.youtube.com/*"]
-    }
   ]
 }