feat: Add tablet landscape orientation support (#490)

- Tablets now support landscape mode, phones remain portrait-only
- Add OrientationAwareActivity base class for orientation management
- Add DeviceUtils.isTablet() for runtime device detection
- Update MainActivity and GeohashPickerActivity to extend OrientationAwareActivity
- Uses multiple detection criteria (screen size, density, configuration)
Fixes #480

app/src/main/java/com/bitchat/android/MainActivity.kt

@@ -3,7 +3,6 @@ package com.bitchat.android
 import android.content.Intent
 import android.os.Bundle
 import android.util.Log
-import androidx.activity.ComponentActivity
 import androidx.activity.OnBackPressedCallback
 import androidx.activity.compose.setContent
 import androidx.activity.enableEdgeToEdge
@@ -15,7 +14,6 @@ import androidx.compose.material3.Scaffold
 import androidx.compose.runtime.*
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.platform.LocalContext
-import androidx.compose.ui.unit.dp
 import androidx.lifecycle.lifecycleScope
 import androidx.lifecycle.ViewModelProvider
 import androidx.lifecycle.repeatOnLifecycle
@@ -39,13 +37,14 @@ import com.bitchat.android.onboarding.PermissionExplanationScreen
 import com.bitchat.android.onboarding.PermissionManager
 import com.bitchat.android.ui.ChatScreen
 import com.bitchat.android.ui.ChatViewModel
+import com.bitchat.android.ui.OrientationAwareActivity
 import com.bitchat.android.ui.theme.BitchatTheme
 import com.bitchat.android.nostr.PoWPreferenceManager
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.launch
 
-class MainActivity : ComponentActivity() {
-    
+class MainActivity : OrientationAwareActivity() {
+
     private lateinit var permissionManager: PermissionManager
     private lateinit var onboardingCoordinator: OnboardingCoordinator
     private lateinit var bluetoothStatusManager: BluetoothStatusManager