feat: Major UI enhancement with BlackRoad brand system

- Add stunning landing page with hero, features, and CTA sections
- Update login/signup pages with dark theme and brand gradients
- Enhance Sidebar with improved navigation and brand colors
- Update AppHeader with search bar, notifications, and user menu
- Add reusable UI components (Button, Card, Input, Badge)
- Add API health and status endpoints
- Apply official BlackRoad brand colors (#FF1D6C hot pink, #F5A623 amber, #2979FF electric blue, #9C27B0 violet)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/(app)/layout.tsx

@@ -33,7 +33,7 @@ export default function AppLayout({
       <Sidebar />
       <div className="flex flex-1 flex-col overflow-hidden">
         <AppHeader />
-        <main className="flex-1 overflow-y-auto bg-gray-50">
+        <main className="flex-1 overflow-y-auto bg-black">
           {children}
         </main>
       </div>