feat(auth): transition from email to phone-based OTP authentication

- Replace Email+Password login with Phone+OTP flow
- Remove RegisterCubit and registration screens (email verification)
- Remove ResetPasswordCubit and reset password screens
- Add phone normalization and international dial code support
- Update LoginCubit with sendCode/resend cooldown logic
- Add new widgets: phone prefix selector, confirm sheet
- Update all auth API endpoints: /otp/send, /phone-session
- Update form inputs: Email -> Phone with E.164 validation
- Update tests for new auth flow

apps/lib/features/auth/data/models/signup_request.dart

@@ -1,37 +1,28 @@
-class SignupStartRequest {
-  final String username;
-  final String email;
-  final String password;
-  final String? inviteCode;
+class OtpSendRequest {
+  final String phone;
 
-  const SignupStartRequest({
-    required this.username,
-    required this.email,
-    required this.password,
-    this.inviteCode,
-  });
+  const OtpSendRequest({required this.phone});
+
+  Map<String, dynamic> toJson() => {'phone': _normalizePhone(phone)};
+}
+
+class PhoneSessionRequest {
+  final String phone;
+  final String token;
+
+  const PhoneSessionRequest({required this.phone, required this.token});
 
   Map<String, dynamic> toJson() => {
-    'username': username,
-    'email': email,
-    'password': password,
-    if (inviteCode != null) 'invite_code': inviteCode,
+    'phone': _normalizePhone(phone),
+    'token': token,
   };
 }
 
-class SignupVerifyRequest {
-  final String email;
-  final String token;
-
-  const SignupVerifyRequest({required this.email, required this.token});
-
-  Map<String, dynamic> toJson() => {'email': email, 'token': token};
-}
-
-class SignupResendRequest {
-  final String email;
-
-  const SignupResendRequest({required this.email});
-
-  Map<String, dynamic> toJson() => {'email': email};
+String _normalizePhone(String input) {
+  var normalized = input.trim();
+  normalized = normalized.replaceAll(RegExp(r'[\s\-\(\)]'), '');
+  if (normalized.startsWith('00') && normalized.length > 2) {
+    return '+${normalized.substring(2)}';
+  }
+  return normalized;
 }