chore(release): v1.25.9 — custom metrics

Renumber the custom-metrics migration to 0223 (the next free slot on the
trunk) and cut the release: version bump, regenerated OpenAPI contract,
service-worker stamp, and CHANGELOG entry.

docs/api/openapi.yaml

@@ -1,7 +1,7 @@
 openapi: 3.1.0
 info:
   title: HealthLog API
-  version: 1.25.8
+  version: 1.25.9
   description: >-
     Self-hosted personal-health-tracking PWA — public API surface for the iOS native client and external ingest.