fix(api): close M5 frontend contract gaps

docs/BACKEND/API_GUIDES/V2/unified-api.md

@@ -104,6 +104,11 @@ Coverage-review request payload may also send:
 
 If `markAsFavorite` is `true`, backend adds that worker to the business favorites list. If `markAsFavorite` is `false`, backend removes them from that list. If `markAsBlocked` is `true`, backend adds that staff member to the business-level blocked list and future apply or assign attempts are rejected until a later review sends `markAsBlocked: false`.
 
+`GET /client/coverage` response notes:
+
+- each shift item includes `locationName` and `locationAddress`
+- each assigned worker item includes `hasReview`
+
 Swap-review routes:
 
 - `GET /client/coverage/swap-requests?status=OPEN`
@@ -163,6 +168,7 @@ The manager is created as an invited business membership. If `hubId` is present,
 
 - `GET /staff/session`
 - `GET /staff/dashboard`
+- `GET /staff/profile/stats`
 - `GET /staff/profile-completion`
 - `GET /staff/availability`
 - `GET /staff/clock-in/shifts/today`
@@ -218,6 +224,21 @@ Example `GET /staff/clock-in/shifts/today` item:
 }
 ```
 
+Example `GET /staff/profile/stats` response:
+
+```json
+{
+  "staffId": "uuid",
+  "totalShifts": 12,
+  "averageRating": 4.8,
+  "ratingCount": 7,
+  "onTimeRate": 91.7,
+  "noShowCount": 1,
+  "cancellationCount": 0,
+  "reliabilityScore": 92.3
+}
+```
+
 ### Staff writes
 
 - `POST /staff/profile/setup`
@@ -296,12 +317,14 @@ These are exposed as direct unified aliases even though they are backed by `core
   - `NFC_REQUIRED`
   - `GEO_REQUIRED`
   - `EITHER`
+- all source-of-truth timestamps are UTC ISO 8601 values. Frontend should convert them to local time for display.
 - For `POST /staff/clock-in` and `POST /staff/clock-out`:
   - send `nfcTagId` when clocking with NFC
   - send `latitude`, `longitude`, and `accuracyMeters` when clocking with geolocation
   - send `proofNonce` and `proofTimestamp` for attendance-proof logging; these are most important on NFC paths
   - send `attestationProvider` and `attestationToken` only when the device has a real attestation result to forward
   - send `overrideReason` only when the worker is bypassing a geofence failure and the shift/hub allows overrides
+  - if the worker is already clocked in, backend returns `409` with code `ALREADY_CLOCKED_IN`
 - `POST /staff/location-streams` is for the background tracking loop after a worker is already clocked in.
 - `GET /client/coverage/incidents` is the review feed for geofence breaches, missing-location batches, and clock-in overrides.
 - `GET /client/coverage/blocked-staff` is the review feed for workers currently blocked by that business.