feat: integrate WebP/AVIF image optimization into build pipeline

- Add sharp dependency for image format conversion
- Generate WebP (quality 80) and AVIF (quality 70) variants for all raster images
- Render <picture> elements with srcset fallbacks (AVIF > WebP > original)
- SVG images remain as <img> without picture wrapper
- Update Dockerfile to install libvips for sharp, copy from public/ dir
- Add nginx cache rules for .webp and .avif files
- Add .gitignore for node_modules, public, dist

Dockerfile

@@ -3,6 +3,9 @@ FROM node:22-alpine AS builder
 
 WORKDIR /app
 
+# Install build dependencies for sharp (libvips)
+RUN apk add --no-cache python3 make g++ vips-dev
+
 # Copy package files and install dependencies
 COPY package*.json ./
 RUN npm ci
@@ -15,12 +18,12 @@ RUN npm run build
 FROM nginx:alpine
 
 # Copy built site
-COPY --from=builder /app/dist /usr/share/nginx/html
+COPY --from=builder /app/public /usr/share/nginx/html
 
 # Copy ads.txt if present at root
-COPY --from=builder /app/ads.txt /usr/share/nginx/html/ads.txt
+COPY --from=builder /app/public/ads.txt /usr/share/nginx/html/ads.txt
 
-# Custom nginx config for SPA/history routing
+# Custom nginx config for SPA/history routing with image format support
 RUN echo 'server { \
     listen 80; \
     server_name localhost; \
@@ -29,7 +32,7 @@ RUN echo 'server { \
     location / { \
         try_files $uri $uri/ /index.html; \
     } \
-    location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg|woff|woff2|ttf|eot)$ { \
+    location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg|woff|woff2|ttf|eot|webp|avif)$ { \
         expires 1y; \
         add_header Cache-Control "public, immutable"; \
     } \