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)

package.json

@@ -35,10 +35,8 @@
     "nodemailer": "^8.0.1",
     "pg": "^8.18.0",
     "prisma": "^7.3.0",
-    "radix-ui": "^1.4.3",
     "react": "19.2.3",
     "react-dom": "19.2.3",
-    "shadcn": "^3.8.3",
     "sonner": "^2.0.7",
     "tailwind-merge": "^3.4.0",
     "tw-animate-css": "^1.4.0",
@@ -54,6 +52,7 @@
     "@types/react-dom": "^19",
     "eslint": "^9",
     "eslint-config-next": "16.1.6",
+    "shadcn": "^3.8.3",
     "tailwindcss": "^4",
     "typescript": "^5"
   },