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

site.webmanifest

@@ -0,0 +1,24 @@
+{
+    "name": "Agencja AI",
+    "short_name": "Agencja AI",
+    "icons": [
+        {
+            "src": "/assets/imgs/favico/48x48.png",
+            "sizes": "48x48",
+            "type": "image/png"
+        },
+        {
+            "src": "/assets/imgs/favico/180x180.png",
+            "sizes": "180x180",
+            "type": "image/png"
+        },
+        {
+            "src": "/assets/imgs/favico/512x512.png",
+            "sizes": "512x512",
+            "type": "image/png"
+        }
+    ],
+    "display": "standalone",
+    "theme_color": "#000000",
+    "background_color": "#000000"
+}