fix: MFA setup completion not updating UI state

Root cause: the MFA status endpoint returned `mfa_enabled` as the JSON
key but the TypeScript MfaStatus interface expected `enabled`. At
runtime, `mfaStatus.value?.enabled` was always `undefined`, so
`isEnabled` was always false — the banner never hid and the method
cards never showed "Geconfigureerd".

Additionally, the auth store had no way to re-fetch /auth/me after
initialization, so `mfaSetupRequired` was never properly refreshed
from the backend after MFA setup.

Fixes:
- Rename `mfa_enabled` → `enabled` in the MFA status endpoint response
  to match the TypeScript type (and the /auth/me MeResource which
  already used `enabled`)
- Add `refreshUser()` to the auth store for post-initialization
  re-fetching of /auth/me
- Call `refreshUser()` in onSetupCompleted so the store reflects the
  backend state without a full page reload
- Update backend tests to match the renamed response key

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

api/tests/Feature/Auth/MfaSetupControllerTest.php

@@ -147,7 +147,7 @@ class MfaSetupControllerTest extends TestCase
         $response->assertOk()
             ->assertJson([
                 'data' => [
-                    'mfa_enabled' => false,
+                    'enabled' => false,
                     'method' => null,
                     'confirmed_at' => null,
                     'backup_codes_remaining' => 0,
@@ -164,7 +164,7 @@ class MfaSetupControllerTest extends TestCase
         $response->assertOk()
             ->assertJson([
                 'data' => [
-                    'mfa_enabled' => true,
+                    'enabled' => true,
                     'method' => 'totp',
                     'backup_codes_remaining' => 10,
                 ],