chore(release): v1.8.4 — medication card accuracy + Insights polish

The medication card reads the schedule engine's next-due (fixes
interval/one-time schedules that never advanced after a dose), logging a
dose confirms itself, Insights status polling is bounded, each Insights
category explains itself inline, medication history shows each dose's
origin, and an idempotent migration adds the app_settings columns that
were only ever applied ad-hoc.

docs/api/openapi.yaml

@@ -1,7 +1,7 @@
 openapi: 3.1.0
 info:
   title: HealthLog API
-  version: 1.8.3
+  version: 1.8.4
   description: >-
     Self-hosted personal-health-tracking PWA — public API surface for the iOS native client and external ingest.