refactor: centralize data connect error handling and resolve build issues across applications

This commit addresses several critical issues across the mobile monorepo:

1. Centralized Error Handling: Integrated DataErrorHandler mixin into all repository implementations, ensuring consistent mapping of Data Connect exceptions to domain AppExceptions.
2. Build Stabilization: Fixed numerous type mismatches, parameter signature errors in widgets (e.g., google_places_flutter itemBuilder), and naming conflicts (StaffSession, FirebaseAuth).
3. Code Quality: Applied 'dart fix' across all modified packages and manually cleared debug print statements and UI clutter.
4. Mono-repo alignment: Standardized Data Connect usage and aliasing ('dc.') for better maintainability.

Signed-off-by: Suriya <suriya@tenext.in>

docs/CENTRALIZED_ERROR_HANDLING_MASTER.md

@@ -19,6 +19,11 @@ I've successfully implemented a **production-ready centralized error handling sy
 - Registered in both Client and Staff apps
 - Ready for Sentry/Crashlytics
 
+**✅ Data Layer Error Handler** (`data_connect` package)
+- `DataErrorHandler` mixin
+- Wraps Data Connect calls
+- Maps `SocketException` and `FirebaseException` to Domain `AppException` (Network/Server)
+
 ### 2. **BLoC Migrations** (2 Complete)
 **✅ ClientAuthBloc** - 4 event handlers migrated
 - Reduced from 173 to 153 lines (-11.6%)