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>

backend/src/services/session.service.js

@@ -210,12 +210,13 @@ export const getCustomerHistory = async (customerId, { page = 1, limit = 20 } =
     FROM chat_sessions cs
     LEFT JOIN mitras m ON m.id = cs.mitra_id
     WHERE cs.customer_id = ${customerId}
-      AND cs.status = ${SessionStatus.COMPLETED}
-    ORDER BY cs.ended_at DESC
+      AND cs.status IN (${SessionStatus.COMPLETED}, ${SessionStatus.CLOSING})
+    ORDER BY COALESCE(cs.ended_at, cs.created_at) DESC
     LIMIT ${limit} OFFSET ${offset}
   `
   const [{ count }] = await sql`
-    SELECT COUNT(*) FROM chat_sessions WHERE customer_id = ${customerId} AND status = ${SessionStatus.COMPLETED}
+    SELECT COUNT(*) FROM chat_sessions WHERE customer_id = ${customerId}
+      AND status IN (${SessionStatus.COMPLETED}, ${SessionStatus.CLOSING})
   `
   return { items, total: Number(count), page, limit }
 }
@@ -231,12 +232,13 @@ export const getMitraHistory = async (mitraId, { page = 1, limit = 20 } = {}) =>
     FROM chat_sessions cs
     INNER JOIN customers c ON c.id = cs.customer_id
     WHERE cs.mitra_id = ${mitraId}
-      AND cs.status = ${SessionStatus.COMPLETED}
-    ORDER BY cs.ended_at DESC
+      AND cs.status IN (${SessionStatus.COMPLETED}, ${SessionStatus.CLOSING})
+    ORDER BY COALESCE(cs.ended_at, cs.created_at) DESC
     LIMIT ${limit} OFFSET ${offset}
   `
   const [{ count }] = await sql`
-    SELECT COUNT(*) FROM chat_sessions WHERE mitra_id = ${mitraId} AND status = ${SessionStatus.COMPLETED}
+    SELECT COUNT(*) FROM chat_sessions WHERE mitra_id = ${mitraId}
+      AND status IN (${SessionStatus.COMPLETED}, ${SessionStatus.CLOSING})
   `
   return { items, total: Number(count), page, limit }
 }