docs: rewrite README.md with project overview and structure

README.md

@@ -1,17 +1,48 @@
-# traccar_client
+# Traccar Client
 
-A new Flutter project.
+Flutter Android app for background GPS location tracking, sending data to a Traccar server.
 
-## Getting Started
+## Build
 
-This project is a starting point for a Flutter application.
+```bash
+flutter build apk --debug
+```
 
-A few resources to get you started if this is your first Flutter project:
+The APK is output to `build/app/outputs/flutter-apk/app-debug.apk`.
 
-- [Learn Flutter](https://docs.flutter.dev/get-started/learn-flutter)
-- [Write your first Flutter app](https://docs.flutter.dev/get-started/codelab)
-- [Flutter learning resources](https://docs.flutter.dev/reference/learning-resources)
+## Project Structure
 
-For help getting started with Flutter development, view the
-[online documentation](https://docs.flutter.dev/), which offers tutorials,
-samples, guidance on mobile development, and a full API reference.
+```
+lib/
+  main.dart                 # App entry, dark theme, routing
+  main_screen.dart          # Tracking toggle + live coordinates
+  permission_screen.dart    # Pre-flight permission setup
+  settings_screen.dart       # Server URL, device ID, accuracy config
+  status_screen.dart        # Event log (LOCATION, SYNC, ERROR, etc.)
+  preferences.dart          # SharedPreferences wrapper
+  bridge/
+    location_bridge.dart   # Dart↔Native MethodChannel (com.traccar.client/tracking)
+
+android/app/src/main/kotlin/com/traccar/traccar_client/
+  BridgeModule.kt           # Method channel handler
+  service/LocationTrackingService.kt
+  location/HeartbeatScheduler.kt  # AlarmManager heartbeat
+  network/TraccarHttpClient.kt    # POST to server
+  network/ConnectivityReceiver.kt
+```
+
+## Configuration
+
+On first launch, `PermissionScreen` guides through:
+1. **Location** — `locationWhenInUse` then `locationAlways` (background)
+2. **Notification** — required for tracking alerts
+3. **Battery** — disable Doze optimization so tracking works reliably
+
+Then set server URL and device ID in Settings before starting tracking.
+
+## Server Request Format
+
+POST to `https://yourserver/?id=DEVICE_ID&lat=...&lon=...&timestamp=...&is_moving=0`
+
+- `is_moving` = `speed > 1.0 m/s` (3.6 km/h threshold)
+- Server URL and device ID come from `Preferences` (configured in Settings screen)