feat: add landing page with pricing, features, hardware kits

Apple-style one-page landing for TankSync Cloud:
- Hero with animated gradient + CTA
- Problem stats (water waste, pump failures)
- Solution with feature checklist
- How it works (3 steps with placeholders)
- 9-feature grid with hover animations
- Tech specs for TX and RX
- Pricing: Free/Home/Pro with auto INR/USD based on timezone
- Hardware kits: Single (7,499) and Dual (11,999)
- Footer with contact, GitHub, YouTube links

Pricing (location-detected):
- India: Free / ₹99/mo / ₹299/mo
- International: Free / $1.99/mo / $4.99/mo

Unauthenticated users see landing page at /.
Login/signup accessible via nav button.

Author: Ravi Singh

pwa/client/src/App.jsx

@@ -15,6 +15,7 @@ import Alerts from './pages/Alerts.jsx';
 import Settings from './pages/Settings.jsx';
 import OTA from './pages/OTA.jsx';
 import LinkDevice from './pages/LinkDevice.jsx';
+import Landing from './pages/Landing.jsx';
 
 export default function App() {
   return (
@@ -25,7 +26,7 @@ export default function App() {
 }
 
 function AppRoutes() {
-  const { user, loading } = useAuth();
+  const { user, loading, needsVerification } = useAuth();
   const location = useLocation();
 
   if (loading) {
@@ -39,12 +40,13 @@ function AppRoutes() {
     );
   }
 
-  if (!user) {
+  if (!user || needsVerification) {
     return (
       <Routes>
+        <Route path="/" element={<Landing />} />
         <Route path="/login" element={<Login />} />
         <Route path="/link" element={<LinkDevice />} />
-        <Route path="*" element={<Navigate to="/login" replace />} />
+        <Route path="*" element={<Navigate to="/" replace />} />
       </Routes>
     );
   }