Phase 3.7: paid pairing flow + returning chat + extension flip

- Backend: payment_sessions + pairing_failures tables; payment.service.js
  and pairing-failure.service.js (new); rewritten pairing.service.js
  (payment-gated blast + targeted "Curhat lagi" + cancel + fallback);
  rewritten extension.service.js (data-driven auto-approve with offline
  safeguard, charge-at-approval); pricing.service.js (extension tiers
  without free trial); mitra-status.service.js (countAvailableMitras
  cached path); 60s sweeper for stale payment sessions
- Backend routes: client.payment.routes, client.mitra-availability.routes,
  internal/failed-pairings.routes; client.chat.routes rewritten for
  payment-gated start + /returning + /cancel + /fallback-to-blast;
  internal/config.routes adds 4 new keys with Valkey invalidate publish
- client_app: mitra-availability poll, payment screen + notifier, pairing
  notifier rewrite (PairingTargetedWaiting + PairingFailed states),
  targeted-waiting overlay + bestie-unavailable dialog, "Curhat lagi"
  CTA, failed-pairing terminal, extension via payment-session
- mitra_app: PairingRequestType enum, returning-chat 20s countdown
  auto-dismiss, extension card "otomatis disetujui" copy
- control_center: 4 new config rows in Settings, Failed Pairings page
  (filter + paginate + action menu), sidebar + route registered
- Test infrastructure: Vitest backend (7/7 pass), Playwright CC (4/4
  pass), Maestro mobile scaffold (CLI install pending)
- Bugs found via Playwright + fixed: LoginPage labels not associated
  with inputs (a11y); backend internal CORS missing PATCH/PUT/DELETE
  in allow-methods (silent settings breakage in browsers since Stage 4)
- Docs: phase3.7.md PRD, phase3.7-plan.md, phase3.7-questions.md (Q&A),
  phase3.7-testing.md (E2E checklist), phase3.7-test-run-2026-05-03.md
  (today's run results)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

client_app/lib/router.dart

@@ -11,12 +11,14 @@ import 'features/auth/screens/set_display_name_screen.dart';
 import 'features/onboarding/onboarding_screen.dart';
 import 'features/splash/splash_screen.dart';
 import 'features/home/home_screen.dart';
+import 'core/constants.dart';
 import 'features/chat/screens/searching_screen.dart';
 import 'features/chat/screens/bestie_found_screen.dart';
 import 'features/chat/screens/no_bestie_screen.dart';
 import 'features/chat/screens/chat_screen.dart';
 import 'features/chat/screens/chat_history_screen.dart';
 import 'features/chat/screens/chat_transcript_screen.dart';
+import 'features/payment/screens/payment_screen.dart';
 
 class RouterNotifier extends ChangeNotifier {
   final Ref _ref;
@@ -96,6 +98,22 @@ GoRouter buildRouter(Ref ref) {
       GoRoute(path: '/auth/set-name', builder: (_, __) => const SetDisplayNameScreen()),
       GoRoute(path: '/auth/force-register', builder: (_, __) => const ForceRegisterScreen()),
       GoRoute(path: '/home', builder: (_, __) => const HomeScreen()),
+      GoRoute(path: '/payment', builder: (context, state) {
+        // Payment screen reachable from
+        //   - Home "Mulai Curhat" CTA  → no extras (general blast follows confirm)
+        //   - Chat history "Curhat lagi" CTA → extras carry targetedMitraId/mitraName
+        //     for the returning-chat flow, plus optional topicSensitivity.
+        final extra = state.extra;
+        if (extra is Map<String, dynamic>) {
+          final topic = extra['topicSensitivity'];
+          return PaymentScreen(
+            targetedMitraId: extra['targetedMitraId'] as String?,
+            mitraName: extra['mitraName'] as String?,
+            topicSensitivity: topic is TopicSensitivity ? topic : TopicSensitivity.regular,
+          );
+        }
+        return const PaymentScreen();
+      }),
       GoRoute(path: '/chat/searching', builder: (_, __) => const SearchingScreen()),
       GoRoute(path: '/chat/found', builder: (context, state) {
         final extra = state.extra as Map<String, dynamic>;