Phase 4 Stage 10 backend: Chat-tab feeds (pending payments + cursor history)

Backend half of Stage 10 — the new Chat tab in the customer app that
replaces /chat/history with a 3-sub-tab list (Aktif / Pembayaran /
Selesai).

- New GET /api/client/payment-sessions/pending — returns the customer's
  pending initial + extension payment sessions. Filter is status='pending'
  AND expires_at > NOW(). Mitra info comes from session_extensions →
  chat_sessions for extension rows, payment_sessions.targeted_mitra_id
  for targeted-curhat-lagi initial rows. TTL reuses the existing
  payment_session_timeout_minutes app_config row (default 20m) — no new
  config row needed since payment is still mocked.

- getCustomerHistory migrated from offset (page/limit) to cursor
  pagination. Cursor is base64url(`<endedAtIso>|<id>`) with id-tiebreak
  in ORDER BY so rows with identical timestamps don't duplicate or skip
  across pages. SELECT now JOINs payment_sessions to surface `mode`
  (chat/call) for the Selesai-row voice-call pill.

- requirement/flow_customer.mermaid.md: new §7 Chat Tab subgraph + Figma
  cross-ref entry for SChatList.

- requirement/phase4-customer-flow-plan.md: Stage 10 plan section. Also
  carries forward earlier uncommitted "Post-Stage-8 corrections" notes
  from the Stage 9 sweep (boot path / SHome1st / onboarding fixes).

Tests: +7 for getCustomerPendingPayments (initial null mitra,
targeted-mitra fill, extension-via-session JOIN, mixed-newest-first,
expired excluded, non-pending excluded, customer scoping). +10 for
cursor history (empty, exact-fit, multi-page walk, same-timestamp
tiebreak, limit clamp, customer scoping, CLOSING+COMPLETED only).

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

backend/src/services/payment.service.js

@@ -304,3 +304,41 @@ export const getPaymentSession = async (id) => {
   `
   return row || null
 }
+
+/**
+ * Phase 4 Stage 10 — Chat Tab Pembayaran feed.
+ *
+ * Returns the customer's pending payment sessions (initial + extension) that
+ * haven't paid AND haven't expired. The `expires_at > NOW()` filter is
+ * defensive: the background sweeper flips stale pending rows to `expired`,
+ * but rows can be stale between sweeps, so we filter inline too.
+ *
+ * Extension rows resolve mitra info via session_extensions → chat_sessions →
+ * mitras. Initial rows fall back to `payment_sessions.targeted_mitra_id`
+ * (set for targeted "Curhat lagi" flows); for general-blast initial rows
+ * the mitra is unknown until pairing succeeds, so mitra fields are null.
+ */
+export const getCustomerPendingPayments = async (customerId) => {
+  const items = await sql`
+    SELECT
+      ps.id,
+      ps.is_extension,
+      ps.amount,
+      ps.duration_minutes,
+      ps.mode,
+      ps.created_at,
+      ps.expires_at,
+      COALESCE(ext_m.id, tgt_m.id)              AS mitra_id,
+      COALESCE(ext_m.display_name, tgt_m.display_name) AS mitra_display_name
+    FROM payment_sessions ps
+    LEFT JOIN session_extensions se ON se.payment_session_id = ps.id
+    LEFT JOIN chat_sessions cs ON cs.id = se.session_id
+    LEFT JOIN mitras ext_m ON ext_m.id = cs.mitra_id
+    LEFT JOIN mitras tgt_m ON tgt_m.id = ps.targeted_mitra_id
+    WHERE ps.customer_id = ${customerId}
+      AND ps.status = ${PaymentSessionStatus.PENDING}
+      AND ps.expires_at > NOW()
+    ORDER BY ps.created_at DESC
+  `
+  return { items, total: items.length }
+}