Phase 4 Stage 6: chat-room countdown UX + voice-call mode pill

Customer chat screen:
- Voice-call header pill (mode == 'call' renders accent-colored pill;
  chat mode renders no pill).
- HaloSnackbar fires once per session at 180s remaining ('sisa 3 menit
  lagi ya 🤍'), driven by the backend session_warning WS event.
- Last-2-min danger styling: timer pill flips to HaloTokens.danger +
  bold JetBrainsMono when remaining <= 120s.
- Floating ChatExpiredBanner widget injected above the input bar when
  remaining hits 0 in closing-grace state. perpanjang -> existing
  pricing bottom sheet.
- pricing_bottom_sheet.dart rewritten to the 5-option layout with
  chat|call mode toggle (mirrors duration-pick from Stage 3).

Mitra chat screen: voice-call header pill only (no countdown UX per PRD).

Backend:
- session.service.js getSessionById JOINs payment_sessions so mode +
  expires_at ship in /api/shared/chat/:id/info.
- session-timer.service.js onThreeMinuteWarning now emits expires_at +
  remaining_seconds for client resync.
- Dev-only POST /internal/_test/force-session-expires-at clears the
  3-min flag, reschedules the timer, and broadcasts WS resync. Lets
  the Maestro flow drive 175s -> 90s -> 0s without waiting live.

New chatRemainingSeconds StreamProvider derived from expiresAt, fed by
session_warning / session_timer / session_expired resync messages
(plan referenced a secondsLeftProvider that didn't actually exist).

Maestro 06_chat_countdown.yaml + force_session_expires_at.js helper.

Out of scope: meet.google.com URL launching - url_launcher isn't a
client_app dependency and message bubbles render plain Text. Defer.

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

backend/src/services/session.service.js

@@ -149,15 +149,20 @@ export const listSessions = async ({ page = 1, limit = 20, status, topic_sensiti
 }
 
 export const getSessionById = async (sessionId) => {
+  // `mode` lives on payment_sessions (chat | call), introduced in Phase 4.1.
+  // The chat header pill needs it, so surface it on every session.info read.
+  // Falls back to 'chat' for pre-3.7 rows where payment_session_id is null.
   const [session] = await sql`
     SELECT cs.id, cs.customer_id, cs.mitra_id, cs.status, cs.topic_sensitivity, cs.topics,
       cs.created_at, cs.paired_at, cs.ended_at, cs.ended_by,
       cs.duration_minutes, cs.price, cs.is_first_session_discount, cs.expires_at, cs.extended_minutes,
+      COALESCE(ps.mode, 'chat') AS mode,
       c.display_name AS customer_display_name,
       m.display_name AS mitra_display_name
     FROM chat_sessions cs
     INNER JOIN customers c ON c.id = cs.customer_id
     LEFT JOIN mitras m ON m.id = cs.mitra_id
+    LEFT JOIN payment_sessions ps ON ps.id = cs.payment_session_id
     WHERE cs.id = ${sessionId}
   `
   return session