Integrate Polkadot.js blockchain with mobile wallet (FAZ 1)

This commit implements the complete blockchain integration for the mobile app's wallet functionality:

**Polkadot.js Integration:**
- Created PolkadotContext for mobile with full blockchain connectivity
- Implemented wallet creation with mnemonic seed phrases
- Added secure key management with AsyncStorage
- Connected to Pezkuwi testnet (wss://beta-rpc.pezkuwi.art)

**WalletScreen Enhancements:**
- Live blockchain balance fetching for HEZ (native token)
- Live balance fetching for PEZ and wUSDT (assets)
- Real-time balance updates every 30 seconds
- Actual send transactions using api.tx.balances.transfer (HEZ)
- Actual send transactions using api.tx.assets.transfer (PEZ, wUSDT)
- Transaction signing with user's keypair
- Loading states and error handling
- Wallet creation flow for new users
- Connect/disconnect wallet functionality

**Bottom Navigation:**
- Created BottomTabNavigator with 5 tabs
- Added WalletScreen with live blockchain integration
- Added BeCitizenScreen (citizenship application)
- Added ReferralScreen (referral program)
- Renamed SettingsScreen to ProfileScreen
- Custom center button for "Be Citizen" feature

**App Structure:**
- Wrapped app with PolkadotProvider in App.tsx
- Updated AppNavigator to use BottomTabNavigator
- Integrated language selection flow with blockchain features

All wallet features now use live blockchain data instead of mock data.

mobile/App.tsx

@@ -3,6 +3,7 @@ import { View, ActivityIndicator, StyleSheet } from 'react-native';
 import { StatusBar } from 'expo-status-bar';
 import { initializeI18n } from './src/i18n';
 import { LanguageProvider } from './src/contexts/LanguageContext';
+import { PolkadotProvider } from './src/contexts/PolkadotContext';
 import AppNavigator from './src/navigation/AppNavigator';
 import { KurdistanColors } from './src/theme/colors';
 
@@ -34,10 +35,12 @@ export default function App() {
   }
 
   return (
-    <LanguageProvider>
-      <StatusBar style="auto" />
-      <AppNavigator />
-    </LanguageProvider>
+    <PolkadotProvider>
+      <LanguageProvider>
+        <StatusBar style="auto" />
+        <AppNavigator />
+      </LanguageProvider>
+    </PolkadotProvider>
   );
 }