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/not-found.tsx

@@ -3,7 +3,6 @@
 import Link from 'next/link';
 import { motion } from 'framer-motion';
 import AnimatedBackground from '@/components/AnimatedBackground';
-import Footer from '@/components/Footer';
 import Logo from '@/components/Logo';
 import { Button } from '@/components/ui/button';
 import { Home } from 'lucide-react';
@@ -28,7 +27,7 @@ export default function NotFound() {
 
           {/* 404 heading */}
           <motion.h1
-            className="text-7xl md:text-9xl font-bold mb-6 bg-clip-text text-transparent bg-gradient-to-r from-purple-400 via-pink-400 to-cyan-400"
+            className="text-7xl md:text-9xl font-bold mb-6 text-primary"
             initial={{ opacity: 0, y: 20 }}
             animate={{ opacity: 1, y: 0 }}
             transition={{ duration: 0.8, delay: 0.2 }}
@@ -71,8 +70,6 @@ export default function NotFound() {
           </motion.div>
         </div>
       </div>
-
-      <Footer />
     </main>
   );
 }