feat: optimize bundle size and improve image loading

- Unify video page components into single VideoPageContent component
  - Reduces ~2300 lines of duplicated code between dashboard and watch pages
  - Uses mode prop ('dashboard' | 'watch') to handle differences

- Move shadcn to devDependencies (CLI tool, not needed at runtime)

- Remove radix-ui meta-package (components already imported individually)

- Replace <img> tags with next/image for automatic optimization
  - Add remotePatterns config for YouTube, Vimeo, Unsplash domains
  - Update video-card.tsx, videos/new/page.tsx, component-example.tsx

- Add next/dynamic for KeyboardShortcutsModal (lazy load on demand)

next.config.ts

@@ -1,7 +1,15 @@
 import type { NextConfig } from "next";
 
 const nextConfig: NextConfig = {
-  /* config options here */
+  images: {
+    remotePatterns: [
+      { protocol: 'https', hostname: 'img.youtube.com' },
+      { protocol: 'https', hostname: 'i.ytimg.com' },
+      { protocol: 'https', hostname: 'i.vimeocdn.com' },
+      { protocol: 'https', hostname: 'vumbnail.com' },
+      { protocol: 'https', hostname: 'images.unsplash.com' },
+    ],
+  },
 };
 
 export default nextConfig;