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/ui/GeohashPickerActivity.kt

@@ -11,7 +11,6 @@ import android.webkit.WebChromeClient
 import android.webkit.WebSettings
 import android.webkit.WebView
 import android.webkit.WebViewClient
-import androidx.activity.ComponentActivity
 import androidx.activity.compose.setContent
 import androidx.compose.foundation.layout.*
 import androidx.compose.foundation.shape.RoundedCornerShape
@@ -45,7 +44,7 @@ import com.bitchat.android.geohash.LocationChannelManager
 import com.bitchat.android.ui.theme.BASE_FONT_SIZE
 
 @OptIn(ExperimentalMaterial3Api::class)
-class GeohashPickerActivity : ComponentActivity() {
+class GeohashPickerActivity : OrientationAwareActivity() {
 
     companion object {
         const val EXTRA_INITIAL_GEOHASH = "initial_geohash"

app/src/main/java/com/bitchat/android/ui/OrientationAwareActivity.kt

@@ -0,0 +1,28 @@
+package com.bitchat.android.ui
+
+import android.content.pm.ActivityInfo
+import android.os.Bundle
+import androidx.activity.ComponentActivity
+import com.bitchat.android.utils.DeviceUtils
+
+/**
+ * Base activity that automatically sets orientation based on device type.
+ * Tablets can rotate to landscape, phones are locked to portrait.
+ */
+abstract class OrientationAwareActivity : ComponentActivity() {
+
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        setOrientationBasedOnDeviceType()
+    }
+
+    private fun setOrientationBasedOnDeviceType() {
+        requestedOrientation = if (DeviceUtils.isTablet(this)) {
+            // Allow all orientations on tablets
+            ActivityInfo.SCREEN_ORIENTATION_UNSPECIFIED
+        } else {
+            // Lock to portrait on phones
+            ActivityInfo.SCREEN_ORIENTATION_PORTRAIT
+        }
+    }
+}