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>

client_app/.maestro/flows/06_chat_countdown.yaml

@@ -0,0 +1,74 @@
+# Stage 6 acceptance: drive a live chat session through the countdown UX
+# in one run.
+#
+# Flow:
+#   1. Customer is on the chat screen of an ACTIVE session (run flow 03 first).
+#   2. Force expires_at = now + 175s → backend fires `session_warning` at 175s
+#      (180s threshold, fudge 5s for clock drift) within ~1s.
+#   3. Verify the 3-min snackbar copy renders.
+#   4. Force expires_at = now + 90s → timer pill flips to danger styling at
+#      remaining <= 120s (well within the 90s window).
+#   5. Force expires_at = now + 0s → expired banner appears above input bar.
+#
+# Pre-req:
+#   1. A live chat session is on screen (paired + active). The simplest way is
+#      to chain this after flow 03_payment_to_chat_happy.yaml.
+#   2. Backend reachable at BACKEND_INTERNAL_URL with NODE_ENV != 'production'.
+#
+# Run (chained):
+#   maestro test client_app/.maestro/flows/03_payment_to_chat_happy.yaml \
+#                client_app/.maestro/flows/06_chat_countdown.yaml
+appId: ${APP_ID_ANDROID}
+env:
+  BACKEND_INTERNAL_URL: http://localhost:3001
+---
+- launchApp:
+    clearState: false
+
+# Step 0: assert we're already on the chat screen (input hint is the landmark).
+- extendedWaitUntil:
+    visible:
+      text: "Ketik Pesan"
+    timeout: 10000
+
+# Step 1: force expires_at to 175s — fires the 3-min warning within ~1s.
+- runScript:
+    file: ../scripts/force_session_expires_at.js
+    env:
+      BACKEND_INTERNAL_URL: ${BACKEND_INTERNAL_URL}
+      SECONDS_FROM_NOW: "175"
+
+# Step 2: verify the 3-min snackbar.
+- extendedWaitUntil:
+    visible:
+      text: "sisa 3 menit lagi"
+    timeout: 5000
+
+# Step 3: force expires_at to 90s — last-2-min danger pill territory.
+- runScript:
+    file: ../scripts/force_session_expires_at.js
+    env:
+      BACKEND_INTERNAL_URL: ${BACKEND_INTERNAL_URL}
+      SECONDS_FROM_NOW: "90"
+
+# Step 4: assert the danger-styled timer pill renders. The pill content is a
+# minutes-and-seconds string ("1m Xd"); we only assert the unit suffix here
+# because the exact seconds drift between assertion and render.
+- extendedWaitUntil:
+    visible:
+      text: "1m"
+    timeout: 5000
+
+# Step 5: force expires_at to 0s — expired banner appears.
+- runScript:
+    file: ../scripts/force_session_expires_at.js
+    env:
+      BACKEND_INTERNAL_URL: ${BACKEND_INTERNAL_URL}
+      SECONDS_FROM_NOW: "0"
+
+# Step 6: verify the floating expired banner + perpanjang CTA.
+- extendedWaitUntil:
+    visible:
+      text: "waktu curhat habis"
+    timeout: 8000
+- assertVisible: "perpanjang"

client_app/.maestro/scripts/force_session_expires_at.js

@@ -0,0 +1,21 @@
+// Force-set the expires_at of the most-recent ACTIVE chat_session by hitting
+// the dev-only /internal/_test/force-session-expires-at endpoint. Used by the
+// Stage 6 maestro flow (06_chat_countdown.yaml) to drive the 3-min snackbar,
+// last-2-min danger pill, and expired banner without waiting in real time.
+//
+// Reads BACKEND_INTERNAL_URL + SECONDS_FROM_NOW from env (Maestro injects them
+// from the flow). The backend re-runs startSessionTimer with the new schedule
+// AND clears the per-session "3-min warning fired" flag so the warning fires
+// again on the new schedule.
+const url = BACKEND_INTERNAL_URL || 'http://localhost:3001'
+const seconds = parseInt(SECONDS_FROM_NOW || '175', 10)
+const resp = http.post(`${url}/internal/_test/force-session-expires-at`, {
+  body: JSON.stringify({ latest: true, seconds_from_now: seconds }),
+  headers: { 'Content-Type': 'application/json' },
+})
+if (resp.status !== 200) {
+  throw new Error(`force-session-expires-at failed (${resp.status}): ${resp.body}`)
+}
+const data = json(resp.body)
+output.SESSION_ID = data.session_id
+output.EXPIRES_AT = data.expires_at