refactor: externalize tool definitions and polish app shell

- Create lib/tools.tsx as single source of truth for all tool metadata
  (title, shortTitle, navTitle, description, summary, icon, etc.)
- Update AppSidebar to render nav from centralized tools list with
  descriptions, remove collapse footer button
- Update AppHeader with sidebar collapse toggle, tool short title,
  and app logo; remove breadcrumbs
- Update AppPage to auto-resolve tool icon from pathname
- Update ToolsGrid/ToolCard to use shared tools data, remove per-card
  gradients for uniform styling
- Add per-tool HTML title via metadata exports (title template in root
  layout)
- Style landing page and 404 headings with primary theme color
- Add Toolbox icon to hero CTA, GitFork icon link in footer
- Remove footer from error page and "View on Dev" buttons
- Extract ColorPage client component for RSC metadata compatibility

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/layout.tsx

@@ -4,7 +4,10 @@ import './globals.css';
 const siteUrl = process.env.NEXT_PUBLIC_SITE_URL || 'http://localhost:3000';
 
 export const metadata: Metadata = {
-  title: 'Kit - Your Creative Toolkit',
+  title: {
+    default: 'Kit - Your Creative Toolkit',
+    template: '%s | Kit',
+  },
   description: 'A curated collection of creative and utility tools for developers and creators. Features file conversion, image editing, and color manipulation.',
   keywords: ['tools', 'utilities', 'file converter', 'image editor', 'color palette', 'creative toolkit', 'convert', 'paint', 'color', 'open source'],
   metadataBase: new URL(siteUrl),