Move template assets to .env-driven generation.

Site metadata, images, favicons, and YouTube settings are now configured via .env and rendered from HTML/manifest templates at dev or container startup.

Co-authored-by: Cursor <cursoragent@cursor.com>

docker-compose.dev.yml

@@ -7,11 +7,9 @@ services:
     build: !reset null
     env_file:
       - .env
-    environment:
-      POST_VIDEO_REDIRECT_URL: ${POST_VIDEO_REDIRECT_URL:-https://www.youtube.com/watch?v=kujXXtoHUbc}
     volumes:
       - ./index.html:/usr/share/nginx/html/index.html:ro
-      - ./config.js:/usr/share/nginx/html/config.js:ro
       - ./site.webmanifest:/usr/share/nginx/html/site.webmanifest:ro
+      - ./config.js:/usr/share/nginx/html/config.js:ro
       - ./assets:/usr/share/nginx/html/assets:ro
       - ./default.conf:/etc/nginx/conf.d/default.conf:ro