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>

apps/mobile/packages/domain/lib/src/exceptions/app_exception.dart

@@ -304,6 +304,24 @@ class UnknownException extends AppException {
   String get messageKey => 'errors.generic.unknown';
 }
 
+/// Thrown when the server returns an error (500, etc.).
+class ServerException extends AppException {
+  const ServerException({String? technicalMessage})
+      : super(code: 'SRV_001', technicalMessage: technicalMessage);
+
+  @override
+  String get messageKey => 'errors.generic.server_error';
+}
+
+/// Thrown when the service is unavailable (Data Connect down).
+class ServiceUnavailableException extends AppException {
+  const ServiceUnavailableException({String? technicalMessage})
+      : super(code: 'SRV_002', technicalMessage: technicalMessage);
+
+  @override
+  String get messageKey => 'errors.generic.service_unavailable';
+}
+
 /// Thrown when user is not authenticated.
 class NotAuthenticatedException extends AppException {
   const NotAuthenticatedException({String? technicalMessage})