Phase 3: session-end UX overhaul + closing-grace cleanup

Promotes the customer-side chat WebSocket to active-session-scoped (driven
by a new `activeSessionProvider`) so home reflects session state in real
time without a per-screen connection. Backend now auto-completes sessions
left in `closing` after a 5-minute grace window so abandoned goodbye flows
don't leave the customer's home permanently locked.

Customer:
- New `activeSessionProvider` (replaces `unread_notifier`) — single source
  of truth for the active session + unread count; polled every 15s.
- Chat WS lifecycle moved to `main.dart` listener on activeSessionProvider.
  Chat screen joins via `connectIfNotConnected`; the new
  `refreshSessionStatus` reconciles flags from the server when re-entering
  an already-connected session (covers missed `sessionClosing`/`sessionExpired`
  WS events).
- Home filters `closing` from the "Sesi Aktif" CTA so a session pending
  goodbye doesn't block "Mulai Curhat".
- Timer-expired UX is a non-dismissible modal (Tutup / Perpanjang) instead
  of an inline bar.
- Early-end goodbye composer gets an amber "Sesi telah ditutup oleh Bestie"
  banner. Goodbye TextEditingController lifted to state so focus changes
  no longer wipe the message.
- Closure provider reset on chat_screen mount to avoid stale
  `ClosureCompleteData` from a previous session leaking into a new view.
- Chat history now lists `closing` sessions with a "Belum ditutup" badge
  that routes to the live chat (goodbye composer) instead of the transcript.

Mitra:
- Same goodbye-controller fix as customer.
- Same chat-history badge + routing for `closing` items.

Backend:
- New `EndedBy.SYSTEM_AUTO_CLOSE` constant.
- `startClosureGraceTimer` extracted in `session-timer.service.js`; wired
  in from `closure.initiateEarlyEnd`, `extension.rejectExtension`, and
  `extension.handleExtensionTimeout`. Cancelled when customer submits
  goodbye.
- Restart recovery (`restoreActiveTimers`) re-arms grace timers and stamps
  any orphaned `closing` rows with `system_auto_close`.
- `getCustomerHistory` / `getMitraHistory` include `closing` alongside
  `completed`; ordering uses `COALESCE(ended_at, created_at)`.

Removed: dead `session_active_screen.dart` (no router entry).

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

client_app/lib/core/pairing/pairing_notifier.dart

@@ -6,6 +6,7 @@ import 'package:web_socket_channel/web_socket_channel.dart';
 import '../api/api_client.dart';
 import '../api/api_client_provider.dart';
 import '../auth/auth_bridge.dart';
+import '../chat/active_session_notifier.dart';
 import '../constants.dart';
 
 part 'pairing_notifier.g.dart';
@@ -148,6 +149,11 @@ class Pairing extends _$Pairing {
       final sessionId = data['session_id'] as String;
       state = PairingBestieFoundData(sessionId: sessionId, mitraName: mitraName);
 
+      // A session now exists for this customer — refresh the shared snapshot
+      // so the home CTA reflects it immediately when the user returns.
+      // ignore: unawaited_futures
+      ref.read(activeSessionProvider.notifier).refresh();
+
       await Future.delayed(const Duration(seconds: 2));
       state = PairingActiveData(sessionId: sessionId, mitraName: mitraName);
     } else if (type == SessionStatus.expired) {

client_app/lib/core/pairing/pairing_notifier.g.dart

@@ -6,7 +6,7 @@ part of 'pairing_notifier.dart';
 // RiverpodGenerator
 // **************************************************************************
 
-String _$pairingHash() => r'a283e74d7cb4244bac74a950205c91d4b2cf3e9a';
+String _$pairingHash() => r'e1c3074239cc4efda99885331ff91b3e0f903c8d';
 
 /// See also [Pairing].
 @ProviderFor(Pairing)