docs: sync from backend 6c01a30 — Gatus /api/health endpoint shipped

- Mark backend work as complete in Gatus Monitoring doc
- Update follow-up issues table with status column
- Add Activity Log entry for 2.6.49

09 - Audits/Activity Log.md

@@ -11,6 +11,17 @@ entries on top. Maintained by agents per the rule in `../AGENTS.md`.
 
 ---
 
+### 2026-05-28 — backend@6c01a30 — Gatus monitoring: GET /api/health endpoint
+
+**Commits:** backend `19f7eb9` → `44579d6` → `6c01a30` (2.6.48 → 2.6.49)
+**Touched:**
+- Backend: `src/services/health/healthCheckService.ts`, `src/services/health/index.ts`, `src/app.ts`, `__tests__/health-check.test.ts`
+**Why:** Implement `GET /api/health` for Gatus monitoring. Exposes 5 checks (db, redis, rnChainRegistry, rnTokenRegistry, rnApi) in a single public endpoint. Status semantics: `ok` | `degraded` | `down` (503 when DB fails). Each check includes `latencyMs`; registry checks include counts. Rate limiter and request logging skip `/api/health`. 5 route-level unit tests cover ok/degraded/down transitions.
+**Verification:** `tsc --noEmit` clean. `npx jest __tests__/health-check.test.ts` — 5/5 pass.
+**Linked docs updated:** [[08 - Operations/Gatus Monitoring - Proposed Config]]
+
+---
+
 ### 2026-05-28 — backend@19f7eb9, frontend@60ee6fb — Task #10: AML screening (Chainalysis, seller-paid, seller opt-in)
 
 **Commits:** backend `441c8be` → `80ba046` → `19f7eb9` (2.6.46 → 2.6.47), frontend `717d5c8` → `b7540f5` → `60ee6fb` (2.6.46 → 2.6.47)