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

src/favicon.svg

@@ -0,0 +1,5 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 64 64" role="img" aria-label="Signal Ledger favicon">
+  <rect width="64" height="64" rx="12" fill="#161616"/>
+  <path d="M16 48V16h10c8.5 0 13 4 13 10.5 0 4.8-2.3 8-6.8 9.6L44 48H33.5l-10.2-11.1H25V48H16zm9-18.2h1.8c4.1 0 6.2-1.5 6.2-4.6 0-2.9-2-4.3-6.1-4.3H25v8.9z" fill="#f5f1e8"/>
+  <rect x="45" y="18" width="4" height="28" fill="#8b1e1e"/>
+</svg>

src/feeds.js

@@ -0,0 +1,26 @@
+export const FEEDS = [
+  {
+    id: 'reuters-world',
+    source: 'Reuters',
+    category: 'World',
+    url: 'https://news.google.com/rss/search?q=site:reuters.com+world&hl=en-US&gl=US&ceid=US:en'
+  },
+  {
+    id: 'ap-headlines',
+    source: 'AP News',
+    category: 'Top Stories',
+    url: 'https://news.google.com/rss/search?q=site:apnews.com&hl=en-US&gl=US&ceid=US:en'
+  },
+  {
+    id: 'bbc-world',
+    source: 'BBC',
+    category: 'World',
+    url: 'https://feeds.bbci.co.uk/news/world/rss.xml'
+  },
+  {
+    id: 'hacker-news-frontpage',
+    source: 'Hacker News',
+    category: 'Technology',
+    url: 'https://hnrss.org/frontpage'
+  }
+];