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/users/data/models/user_response.dart

@@ -1,14 +1,14 @@
 class UserResponse {
   final String id;
   final String username;
-  final String? email;
+  final String? phone;
   final String? avatarUrl;
   final String? bio;
 
   const UserResponse({
     required this.id,
     required this.username,
-    this.email,
+    this.phone,
     this.avatarUrl,
     this.bio,
   });
@@ -17,7 +17,7 @@ class UserResponse {
     return UserResponse(
       id: json['id'] as String,
       username: json['username'] as String,
-      email: json['email'] as String?,
+      phone: json['phone'] as String?,
       avatarUrl: json['avatar_url'] as String?,
       bio: json['bio'] as String?,
     );