docs: complete code-reality alignment for remaining docs + reconcile issue set

Remaining docs updated to match code (the docs that the first pass had not covered):
- Flows: Chat, Referral, Rating, Registration, Google OAuth, Negotiation, Payout,
  Trezor Safekeeping — corrected endpoints, socket events, status enums, auth gaps
- API Reference: User API, Trezor API — admin route prefix/verb/status corrections,
  added undocumented endpoints (ton-proof challenge, profile email verify,
  GET /trezor/account, POST /trezor/verify-operation)
- Data Models: Chat, Notification, Payment, PointTransaction, User — corrected
  enums (PaymentProvider, escrowState, PointTransaction.type, User.status),
  90-day notification TTL, soft-delete semantics, wallet fields

Trezor "zero frontend" finding (audit C31/C32) corrected as STALE:
- Verified current code HAS a full frontend Trezor implementation (admin/trezor
  page, TrezorSettingsView, trezorConnector via @trezor/connect-web,
  TrezorSignDialog, actions/trezor.ts building the {message,signature} object)
- Fixed Trezor Safekeeping Flow doc (removed false "no frontend" warnings)
- Reclassified ISSUE-012 as invalid/superseded with explanation

Issue set reconciled to a single canonical numbering (ISSUE-001..054):
- Adopted the comprehensive 51-issue set (long-slug, fully indexed)
- Removed 35 superseded short-slug duplicates from the first pass
- Removed a duplicate ISSUE-046 file
- Added 3 issues the 51-set lacked: ISSUE-052 (completed-not-counted-in-stats),
  ISSUE-053 (axios 401-only interceptor), ISSUE-054 (rate limiter counts all attempts)
- Regenerated Issues Index: 53 open (14 critical, 39 major) + 1 invalid

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

04 - Flows/Notification Flow.md

@@ -65,6 +65,10 @@ Cross-cutting flow that powers the bell icon, toast pop-ups, badge counters, and
    - `Notification.findOneAndUpdate({ _id, userId }, { isRead: true, readAt: now })`.
    - After updating, the backend emits `unread-count-update` to `user-{userId}` so all open tabs (and other devices) immediately sync their badge counter.
 
+### Purchase request status coverage gap
+
+`NotificationService.notifyRequestStatusChanged` handles many purchase-request statuses but does **not** emit notifications for `pending_payment` or `seller_paid`. If a buyer moves to `pending_payment` or a seller is marked `seller_paid`, no notification is created. This is a known coverage gap; add dedicated helper methods (or extend the switch-case) if those transitions need to surface to recipients.
+
 ### Preferences
 
 - `User.preferences.notifications` (in the User schema) can hold per-category opt-outs (`emailNotifications`, `pushNotifications`, etc.). The current implementation does not enforce preferences at send-time — all enabled notifications fire. Add a check in `createNotification` to short-circuit when the user has opted out of a category.