Document PostHog dart-define configuration

mobile/README.md

@@ -67,6 +67,20 @@ static String _baseUrl = 'http://localhost:3000';
 static String _baseUrl = 'https://your-sure-server.com';
 ```
 
+### 6. (Optional) Configure PostHog Session Recording
+
+PostHog is configured with **compile-time** Dart defines (not `.env`):
+
+```bash
+flutter run \
+  --dart-define=POSTHOG_API_KEY=phc_your_project_key \
+  --dart-define=POSTHOG_HOST=https://us.i.posthog.com
+```
+
+- `POSTHOG_API_KEY` is required to enable PostHog.
+- `POSTHOG_HOST` is optional and defaults to `https://us.i.posthog.com`.
+- If `POSTHOG_API_KEY` is not passed, the app logs that PostHog is disabled and continues normally.
+
 ### 5. Run the App
 
 ```bash

mobile/lib/main.dart

@@ -17,10 +17,12 @@ import 'services/api_config.dart';
 import 'services/connectivity_service.dart';
 import 'services/log_service.dart';
 import 'services/preferences_service.dart';
+import 'services/posthog_service.dart';
 
 void main() async {
   WidgetsFlutterBinding.ensureInitialized();
   await ApiConfig.initialize();
+  await PostHogService.initialize();
 
   // Add initial log entry
   LogService.instance.info('App', 'Sure app starting...');

mobile/lib/services/posthog_service.dart

@@ -0,0 +1,33 @@
+import 'package:posthog_flutter/posthog_flutter.dart';
+
+import 'log_service.dart';
+
+class PostHogService {
+  PostHogService._();
+
+  static const String _apiKey = String.fromEnvironment('POSTHOG_API_KEY');
+  static const String _host = String.fromEnvironment(
+    'POSTHOG_HOST',
+    defaultValue: 'https://us.i.posthog.com',
+  );
+
+  static Future<void> initialize() async {
+    if (_apiKey.isEmpty) {
+      LogService.instance.info(
+        'PostHog',
+        'PostHog disabled: POSTHOG_API_KEY is not configured.',
+      );
+      return;
+    }
+
+    final config = PostHogConfig(_apiKey, host: _host);
+    config.sessionReplay = true;
+
+    await Posthog().setup(config);
+
+    LogService.instance.info(
+      'PostHog',
+      'PostHog initialized with session replay enabled.',
+    );
+  }
+}

mobile/pubspec.yaml

@@ -26,6 +26,7 @@ dependencies:
   package_info_plus: ^8.0.0
   local_auth: ^2.3.0
   flutter_markdown: ^0.7.2
+  posthog_flutter: ^5.24.2
 
 dev_dependencies:
   flutter_test: