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/main.dart

@@ -4,6 +4,8 @@ import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'core/api/api_client_provider.dart';
 import 'core/auth/auth_notifier.dart';
+import 'core/chat/active_session_notifier.dart';
+import 'core/chat/chat_notifier.dart';
 import 'core/notifications/notification_service.dart';
 import 'firebase_options.dart';
 import 'router.dart';
@@ -45,10 +47,33 @@ class _AppState extends ConsumerState<App> {
 
   @override
   Widget build(BuildContext context) {
+    // FCM registration on auth.
     ref.listen(authProvider, (prev, next) {
       final data = next.valueOrNull;
       if (data is AuthAuthenticatedData || data is AuthAnonymousData) {
         _registerFcmToken();
+      } else {
+        // Logged out (or initial) — ensure the chat WS is closed.
+        ref.read(chatProvider.notifier).disconnect();
+      }
+    });
+
+    // Global chat WebSocket lifecycle: connect whenever the user has an
+    // active session, regardless of which screen is mounted. The chat screen
+    // only joins this connection — it doesn't own it. FCM remains the
+    // background-only fallback.
+    ref.listen(activeSessionProvider, (prev, next) {
+      final snapshot = next.valueOrNull;
+      final notifier = ref.read(chatProvider.notifier);
+      if (snapshot == null || !snapshot.hasSession) {
+        if (notifier.connectedSessionId != null) {
+          notifier.disconnect();
+        }
+        return;
+      }
+      final sessionId = snapshot.sessionId;
+      if (sessionId != null && notifier.connectedSessionId != sessionId) {
+        notifier.connectIfNotConnected(sessionId);
       }
     });