feat: add CI/CD pipeline with Docker + Nginx

- Add Gitea Actions workflow for auto-deploy on push to main
- Add Dockerfile (nginx:alpine based, with layer caching)
- Add nginx.conf (gzip, autoindex, static caching)
- Add .dockerignore
- Migrate cache.html → cache/index.html for directory-based routing

nginx.conf

@@ -0,0 +1,29 @@
+server {
+    listen 80;
+    server_name _;
+    root /usr/share/nginx/html;
+    index index.html;
+
+    # Gzip compression
+    gzip on;
+    gzip_types text/plain text/css application/javascript application/json image/svg+xml;
+    gzip_min_length 256;
+
+    # Static assets caching
+    location ~* \.(css|js|png|jpg|jpeg|gif|ico|svg|woff2|ttf)$ {
+        expires 7d;
+        add_header Cache-Control "public, no-transform";
+    }
+
+    # Auto-index at root for listing available pages
+    location / {
+        autoindex on;
+        autoindex_exact_size off;
+        autoindex_localtime on;
+    }
+
+    # Each subdirectory serves its page
+    location ~ ^/([^/]+)/ {
+        try_files $uri $uri/ /$1/index.html;
+    }
+}