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/test/core/startup/auth_session_bootstrapper_test.dart

@@ -52,7 +52,7 @@ void main() {
 
     await bootstrapper.syncForAuthState(
       const AuthAuthenticated(
-        user: AuthUser(id: 'u1', email: 'a@test.com'),
+        user: AuthUser(id: 'u1', phone: 'a@test.com'),
       ),
     );
 
@@ -68,7 +68,7 @@ void main() {
 
     await bootstrapper.syncForAuthState(
       const AuthAuthenticated(
-        user: AuthUser(id: 'u1', email: 'a@test.com'),
+        user: AuthUser(id: 'u1', phone: 'a@test.com'),
       ),
     );
 
@@ -84,7 +84,7 @@ void main() {
 
     await bootstrapper.syncForAuthState(
       const AuthAuthenticated(
-        user: AuthUser(id: 'u1', email: 'a@test.com'),
+        user: AuthUser(id: 'u1', phone: 'a@test.com'),
       ),
     );