Remove Firebase and Google Calendar integration

This commit removes all Firebase and Google Calendar dependencies and
logic. - Deletes all Firebase-related files and code
(firebase_options.dart, Firebase imports, etc.) - Removes Google
Calendar sync and related UI - Refactors authentication to use only
API-based login/register/logout - Updates profile and statistics
features to use API service and current user - Cleans up unused imports
and code paths - Updates UI and Bloc logic to reflect API-only
authentication and user management

Author: Dibbiii

lib/app/layouts/widgets/plan_sheet/calendar_time_dialog.dart

@@ -3,12 +3,10 @@ import 'package:flutter/material.dart';
 class CalendarTimeDialog extends StatefulWidget {
   final String initialStart;
   final String initialEnd;
-  final bool isGoogleCalendarEvent;
 
   const CalendarTimeDialog({
     this.initialStart = '',
     this.initialEnd = '',
-    required this.isGoogleCalendarEvent,
     super.key,
   });