feat: add admin login page and authentication API

- Created a new login page for admin access at frontend/admin/login/index.html.
- Implemented form submission with error handling for login credentials.
- Updated frontend/index.html to mute the video player and removed unnecessary Alpine.js data binding.
- Enhanced manifest URL resolution in frontend/src/main.ts to include cache-busting parameters.
- Modified vite.config.ts to include the new admin login page in the build process.
- Updated nginx.conf to handle admin login routing, authentication, and API proxying for admin actions.

.env.example

@@ -19,6 +19,12 @@ MEDIA_DOMAIN=media.linearvoid.tv
 VITE_PUBLIC_APP_URL=https://linearvoid.tv
 VITE_PUBLIC_WS_URL=wss://linearvoid.tv/ws
 VITE_PUBLIC_HLS_URL=https://media.linearvoid.tv/hls/playlist.m3u8
+VITE_PUBLIC_ADMIN_DEFAULT_MODERATOR=admin
+VITE_PUBLIC_ADMIN_DEFAULT_ROOM=main
+VITE_PUBLIC_ADMIN_MODERATION_LOG_LIMIT=50
+ADMIN_USERNAME=admin
+ADMIN_PASSWORD=change-me
+ADMIN_SESSION_TTL_HOURS=12
 # Optional direct-local fallback when bypassing the public proxy:
 # VITE_PUBLIC_APP_URL=http://localhost
 # VITE_PUBLIC_WS_URL=ws://localhost/ws