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/(app)/favicon/page.tsx

@@ -1,14 +1,17 @@
-'use client';
-
-import * as React from 'react';
+import type { Metadata } from 'next';
 import { AppPage } from '@/components/layout/AppPage';
 import { FaviconGenerator } from '@/components/favicon/FaviconGenerator';
+import { getToolByHref } from '@/lib/tools';
+
+const tool = getToolByHref('/favicon')!;
+
+export const metadata: Metadata = { title: tool.title };
 
 export default function FaviconPage() {
   return (
     <AppPage
-      title="Favicon Generator"
-      description="Create a complete set of icons for your website including PWA manifest and HTML code."
+      title={tool.title}
+      description={tool.description}
     >
       <FaviconGenerator />
     </AppPage>