v2.1.0: Add floating window overlay functionality

Major Features:
- Floating overlay window with system-level persistence
- Split decimal display (main speed prominent, decimal smaller/faded)
- Optimized content sizing for maximum readability
- Navigation icon trigger for overlay activation
- Multiple close options (overlay button + long-press navigation)

Technical Implementation:
- Added flutter_overlay_window dependency
- Android SYSTEM_ALERT_WINDOW permissions
- Overlay service configuration in AndroidManifest
- Enhanced flex ratios for better space utilization
- BoxFit.contain for improved content scaling

UX Improvements:
- Streamlined overlay launch (removed permission prompts)
- Cleaner visual hierarchy with split speed display
- Responsive design for both portrait and landscape
- Professional overlay styling matching app theme

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

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

android/app/src/main/AndroidManifest.xml

@@ -5,8 +5,10 @@
     <!-- Optional: for background location access -->
     <uses-permission android:name="android.permission.ACCESS_BACKGROUND_LOCATION" />
     
-    <!-- TODO: Enable for display-over-apps functionality -->
-    <!-- <uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" /> -->
+    <!-- Overlay window permissions for floating speedometer -->
+    <uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />
+    <uses-permission android:name="android.permission.FOREGROUND_SERVICE" />
+    <uses-permission android:name="android.permission.FOREGROUND_SERVICE_SPECIAL_USE" />
     
     <application
         android:label="Speedo"
@@ -34,6 +36,12 @@
                 <category android:name="android.intent.category.LAUNCHER"/>
             </intent-filter>
         </activity>
+        
+        <!-- Service for overlay window -->
+        <service
+            android:name="flutter.overlay.window.flutter_overlay_window.OverlayService"
+            android:exported="false" />
+        
         <!-- Don't delete the meta-data below.
              This is used by the Flutter tool to generate GeneratedPluginRegistrant.java -->
         <meta-data