feat: Implement centralized error handling with ErrorService; replace print statements with logging in services and blocs

feat: Add ErrorContent widget for displaying error messages in dialogs and bottom sheets
refactor: Update GroupBloc and GroupRepository to utilize ErrorService for error logging
refactor: Enhance user and trip services to log errors using ErrorService
refactor: Clean up debug print statements in GroupContent and related components

lib/main.dart

@@ -1,6 +1,7 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:firebase_core/firebase_core.dart';
+import 'package:travel_mate/services/error_service.dart';
 import 'blocs/auth/auth_bloc.dart';
 import 'blocs/auth/auth_event.dart';
 import 'blocs/auth/auth_state.dart';
@@ -69,6 +70,7 @@ class MyApp extends StatelessWidget {
           builder: (context, themeState) {
             return MaterialApp(
               title: 'Travel Mate',
+              navigatorKey: ErrorService.navigatorKey,
               themeMode: themeState.themeMode,
               theme: ThemeData(
                 colorScheme: ColorScheme.fromSeed(