feat: add frontend as flat files (was submodule)

frontend/Dockerfile

@@ -0,0 +1,66 @@
+# --- Build stage ---
+FROM node:18-alpine AS build
+
+# Environment: 'dev' or 'prod' (controls theming)
+ARG VITE_ENV=prod
+ENV VITE_ENV=$VITE_ENV
+
+# Game server WebSocket URL (Colyseus)
+ARG VITE_GAME_SERVER_URL
+ENV VITE_GAME_SERVER_URL=$VITE_GAME_SERVER_URL
+
+WORKDIR /app
+
+COPY package*.json ./
+RUN npm ci
+
+COPY . .
+RUN npm run build
+
+# --- Production stage ---
+FROM nginx:alpine
+
+# Copy built assets
+COPY --from=build /app/dist /usr/share/nginx/html
+
+# Copy Unity build if present
+COPY --from=build /app/public/unity-build /usr/share/nginx/html/unity-build
+
+# Nginx config for SPA + gzip precompressed Unity files
+RUN cat > /etc/nginx/conf.d/default.conf << 'EOF'
+server {
+    listen 80;
+    server_name _;
+    root /usr/share/nginx/html;
+    index index.html;
+
+    gzip on;
+    gzip_types text/plain text/css application/json application/javascript text/xml application/xml text/javascript application/wasm;
+
+    location /unity-build/Build/ {
+        types {
+            application/javascript  js;
+            application/wasm        wasm;
+            application/octet-stream data;
+        }
+        add_header Cache-Control "no-cache, must-revalidate";
+        gzip on;
+        gzip_min_length 1000;
+        gzip_types application/javascript application/wasm application/octet-stream;
+    }
+
+    # Aggressive cache for hashed Vite assets (NOT Unity build files)
+    location ~* ^(?!/unity-build/).*\.(js|css|png|jpg|jpeg|gif|ico|svg|woff2?)$ {
+        expires 1y;
+        add_header Cache-Control "public, immutable";
+    }
+
+    location / {
+        try_files $uri $uri/ /index.html;
+    }
+}
+EOF
+
+EXPOSE 80
+
+CMD ["nginx", "-g", "daemon off;"]