Phase 7 - Added Firebase layer

lib/data/session/session_service.dart

@@ -1,8 +1,10 @@
 import 'dart:io';
+import 'package:flutter/foundation.dart';
 import 'package:path/path.dart' as path;
 import 'package:path_provider/path_provider.dart';
 import '../local/local_storage_service.dart';
 import '../sync/sync_engine.dart';
+import '../firebase/firebase_service.dart';
 import 'models/user.dart';
 
 /// Exception thrown when session operations fail.
@@ -37,6 +39,9 @@ class SessionService {
   /// Sync engine for coordinating sync operations (optional).
   final SyncEngine? _syncEngine;
 
+  /// Firebase service for optional cloud sync (optional).
+  final FirebaseService? _firebaseService;
+
   /// Map of user IDs to their session storage paths.
   final Map<String, String> _userDbPaths = {};
 
@@ -53,15 +58,18 @@ class SessionService {
   /// 
   /// [localStorage] - Local storage service for data persistence.
   /// [syncEngine] - Optional sync engine for coordinating sync operations.
+  /// [firebaseService] - Optional Firebase service for cloud sync.
   /// [testDbPath] - Optional database path for testing.
   /// [testCacheDir] - Optional cache directory for testing.
   SessionService({
     required LocalStorageService localStorage,
     SyncEngine? syncEngine,
+    FirebaseService? firebaseService,
     String? testDbPath,
     Directory? testCacheDir,
   })  : _localStorage = localStorage,
         _syncEngine = syncEngine,
+        _firebaseService = firebaseService,
         _testDbPath = testDbPath,
         _testCacheDir = testCacheDir;
 
@@ -101,6 +109,16 @@ class SessionService {
       // Create user-specific storage paths
       await _setupUserStorage(user);
 
+      // Sync with Firebase if enabled
+      if (_firebaseService != null && _firebaseService!.isEnabled) {
+        try {
+          await _firebaseService!.syncItemsFromFirestore(user.id);
+        } catch (e) {
+          // Log error but don't fail login - offline-first behavior
+          debugPrint('Warning: Failed to sync from Firebase on login: $e');
+        }
+      }
+
       // Set as current user
       _currentUser = user;
 
@@ -123,6 +141,16 @@ class SessionService {
     try {
       final userId = _currentUser!.id;
 
+      // Sync to Firebase before logout if enabled
+      if (_firebaseService != null && _firebaseService!.isEnabled) {
+        try {
+          await _firebaseService!.syncItemsToFirestore(userId);
+        } catch (e) {
+          // Log error but don't fail logout - offline-first behavior
+          debugPrint('Warning: Failed to sync to Firebase on logout: $e');
+        }
+      }
+
       // Clear user-specific data if requested
       if (clearCache) {
         await _clearUserData(userId);