init: static frontend for agency-ai.dev — nginx + YouTube intro video

Static landing page served via nginx 1.27 Alpine container.
Features:
- Fullscreen background image visible from first paint
- YouTube intro video overlay (iframe API, lazy loaded)
- PWA manifest with favicons (48x48, 180x180, 512x512)
- SEO meta tags (OG, Twitter Cards, canonical URL)
- Safety timeout: falls back to static image if YouTube fails

Infrastructure:
- Dockerfile: nginx 1.27 Alpine with custom default.conf
  (gzip, cache headers, security headers X-Frame-Options/nosniff)
- docker-compose.yml: local dev on FRONTEND_PORT (default 8080)
- docker-compose-example/: Dokploy deployment via runtime git clone
  from Gitea, resource limits (256M RAM, 0.5 CPU)

Files:
- index.html: main page with inline CSS + JS (YouTube iframe API)
- default.conf: nginx config (gzip, caching, security headers)
- site.webmanifest: PWA manifest
- assets/imgs/: background image + favicons
- .env.example: FRONTEND_PORT template

default.conf

@@ -0,0 +1,35 @@
+server {
+    listen 80;
+    server_name _;
+
+    root /usr/share/nginx/html;
+    index index.html;
+
+    # Gzip compression
+    gzip on;
+    gzip_types text/plain text/css application/json application/javascript text/xml application/xml image/svg+xml;
+    gzip_min_length 1024;
+
+    # Main page
+    location / {
+        try_files $uri $uri/ /index.html;
+    }
+
+    # Web app manifest
+    location = /site.webmanifest {
+        default_type application/manifest+json;
+        expires 30d;
+        add_header Cache-Control "public, immutable";
+    }
+
+    # Assets - long cache for images
+    location /assets/ {
+        expires 30d;
+        add_header Cache-Control "public, immutable";
+        try_files $uri =404;
+    }
+
+    # Security headers
+    add_header X-Frame-Options SAMEORIGIN always;
+    add_header X-Content-Type-Options nosniff always;
+}