feat(01-08): enhance signup page with comprehensive error handling

- Connected to AuthProvider for real registration
- Added specific error messages for different exception types
- Implemented password mismatch validation before submission
- Added error message display with proper styling
- Enhanced form validation with empty field checks
- Added accessibility error announcements via Semantics
- Connected to real registration flow instead of simulation
- Added success message with quick navigation to login
- Included terms agreement validation with clear error message

lib/features/authentication/presentation/pages/signup_page.dart

@@ -1,26 +1,27 @@
 import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:go_router/go_router.dart';
 import '../widgets/auth_form.dart';
 import '../widgets/auth_button.dart';
+import '../../../../providers/auth_provider.dart';
+import '../../../../core/errors/auth_exceptions.dart';
 
 /// Sign up screen with user registration
-class SignupPage extends StatefulWidget {
+class SignupPage extends ConsumerStatefulWidget {
   const SignupPage({super.key});
 
   @override
-  State<SignupPage> createState() => _SignupPageState();
+  ConsumerState<SignupPage> createState() => _SignupPageState();
 }
 
-class _SignupPageState extends State<SignupPage> {
+class _SignupPageState extends ConsumerState<SignupPage> {
   final _formKey = GlobalKey<FormState>();
   final _emailController = TextEditingController();
   final _passwordController = TextEditingController();
   final _confirmPasswordController = TextEditingController();
   
   bool _isLoading = false;
-  String? _emailError;
+  String? _errorMessage;
-  String? _passwordError;
-  String? _confirmPasswordError;
   bool _agreedToTerms = false;
 
   @override
@@ -83,35 +84,69 @@ class _SignupPageState extends State<SignupPage> {
                     email: _emailController.text,
                     onEmailChanged: (value) {
                       setState(() {
-                        _emailError = null;
+                        _errorMessage = null;
                         _emailController.text = value;
                       });
                     },
-                    emailError: _emailError,
+                    emailError: null,
                     password: _passwordController.text,
                     onPasswordChanged: (value) {
                       setState(() {
-                        _passwordError = null;
+                        _errorMessage = null;
                         _passwordController.text = value;
                       });
                     },
-                    passwordError: _passwordError,
+                    passwordError: null,
                     confirmPassword: _confirmPasswordController.text,
                     onConfirmPasswordChanged: (value) {
                       setState(() {
-                        _confirmPasswordError = null;
+                        _errorMessage = null;
                         _confirmPasswordController.text = value;
                       });
                     },
-                    confirmPasswordError: _confirmPasswordError,
+                    confirmPasswordError: null,
                     onSubmit: _handleSignup,
                     submitButtonText: 'Create Account',
                     isLoading: _isLoading,
                     autofocusEmail: true,
-                  ),
+                   ),
-                  const SizedBox(height: 16),
+                   const SizedBox(height: 16),
-                  
+                   
-                  // Terms and conditions checkbox
+                   // Error message display
+                   if (_errorMessage != null) ...[
+                     Container(
+                       padding: const EdgeInsets.all(12),
+                       decoration: BoxDecoration(
+                         color: Theme.of(context).colorScheme.errorContainer,
+                         borderRadius: BorderRadius.circular(8),
+                         border: Border.all(
+                           color: Theme.of(context).colorScheme.error,
+                           width: 1,
+                         ),
+                       ),
+                       child: Row(
+                         children: [
+                           Icon(
+                             Icons.error_outline,
+                             size: 20,
+                             color: Theme.of(context).colorScheme.error,
+                           ),
+                           const SizedBox(width: 8),
+                           Expanded(
+                             child: Text(
+                               _errorMessage!,
+                               style: Theme.of(context).textTheme.bodyMedium?.copyWith(
+                                 color: Theme.of(context).colorScheme.onErrorContainer,
+                               ),
+                             ),
+                           ),
+                         ],
+                       ),
+                     ),
+                     const SizedBox(height: 16),
+                   ],
+                   
+                   // Terms and conditions checkbox
                   _buildTermsCheckbox(),
                   const SizedBox(height: 24),
                   
@@ -225,22 +260,112 @@ class _SignupPageState extends State<SignupPage> {
   Future<void> _handleSignup() async {
     // Clear previous errors
     setState(() {
-      _emailError = null;
+      _errorMessage = null;
-      _passwordError = null;
-      _confirmPasswordError = null;
     });
 
+    // Get form values
+    final email = _emailController.text.trim();
+    final password = _passwordController.text;
+    final confirmPassword = _confirmPasswordController.text;
+
     // Validate terms agreement
     if (!_agreedToTerms) {
-      ScaffoldMessenger.of(context).showSnackBar(
+      setState(() {
-        const SnackBar(
+        _errorMessage = 'Please agree to Terms of Service and Privacy Policy';
-          content: Text('Please agree to the Terms of Service and Privacy Policy'),
+      });
-          duration: Duration(seconds: 3),
-        ),
-      );
       return;
     }
 
+    // Check password match before form validation
+    if (password != confirmPassword) {
+      setState(() {
+        _errorMessage = 'Passwords do not match. Please ensure both passwords are identical.';
+      });
+      return;
+    }
+
+    // Validate form
+    if (!_formKey.currentState!.validate()) {
+      return;
+    }
+
+    // Check for empty fields
+    if (email.isEmpty || password.isEmpty || confirmPassword.isEmpty) {
+      setState(() {
+        _errorMessage = 'Please fill in all required fields';
+      });
+      return;
+    }
+
+    // Show loading state
+    setState(() {
+      _isLoading = true;
+    });
+
+    try {
+      final authProvider = ref.read(authProvider.notifier);
+      await authProvider.signUp(email, password);
+      
+      if (mounted) {
+        ScaffoldMessenger.of(context).showSnackBar(
+          SnackBar(
+            content: const Text('Account created successfully! Please sign in.'),
+            duration: const Duration(seconds: 3),
+            backgroundColor: Colors.green,
+            action: SnackBarAction(
+              label: 'Sign In',
+              onPressed: () => context.go('/login'),
+            ),
+          ),
+        );
+        
+        // Navigate to login page after a short delay
+        Future.delayed(const Duration(seconds: 1), () {
+          if (mounted) {
+            context.go('/login');
+          }
+        });
+      }
+    } catch (e) {
+      if (mounted) {
+        setState(() {
+          _isLoading = false;
+          _errorMessage = _mapErrorToUserFriendlyMessage(e);
+        });
+        
+        // Announce error for accessibility
+        _announceErrorForAccessibility(_errorMessage!);
+      }
+    }
+  }
+
+  /// Maps authentication exceptions to user-friendly error messages
+  String _mapErrorToUserFriendlyMessage(Object error) {
+    if (error is EmailAlreadyInUseException) {
+      return 'This email address is already registered. Please use a different email or try signing in.';
+    } else if (error is WeakPasswordException) {
+      return 'Password is too weak. Please use a stronger password with at least 8 characters, including uppercase, lowercase, and numbers.';
+    } else if (error is InvalidCredentialsException) {
+      return 'Invalid email format. Please enter a valid email address.';
+    } else if (error is NetworkException) {
+      return 'Network connection failed. Please check your internet connection and try again.';
+    } else if (error is TooManyRequestsException) {
+      return 'Too many registration attempts. Please wait a moment and try again.';
+    } else if (error is AuthDisabledException) {
+      return 'Account registration is currently disabled. Please try again later.';
+    } else if (error is AuthException) {
+      return error.message;
+    } else {
+      return 'Registration failed. Please try again or contact support if the problem persists.';
+    }
+  }
+
+  /// Announces error message for screen readers
+  void _announceErrorForAccessibility(String errorMessage) {
+    // Use Semantics to announce error for screen readers
+    SemanticsService.announce(errorMessage, TextDirection.ltr);
+  }
+
     // Validate form
     if (!_formKey.currentState!.validate()) {
       return;