Update CHANGELOG for version 1.9.1

Added details for version 1.9.1, including health endpoint and Docker healthcheck update.

Author: kroeberd

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## [1.9.1] — 2026-05-16
 
+### 1.9.1 — Missed v1.9.0 items: health endpoint, silent failures, error UX
+
 ### Added: `GET /api/health`
 Lightweight liveness probe for Docker `HEALTHCHECK` and uptime monitors. Returns `{"status":"ok","version":"..."}` without any DB access.