chore(release): v1.28.9 — document chat in the coach dialog

Chatting about a document opens the coach chat dialog scoped to that document,
entered from a neutral icon in the document's top-right (matching insights),
instead of a separate inline panel. The document chat's stricter footing is
unchanged — one document only, no health-record context, no tools, plain text.

docs/api/openapi.yaml

@@ -1,7 +1,7 @@
 openapi: 3.1.0
 info:
   title: HealthLog API
-  version: 1.28.8
+  version: 1.28.9
   description: >-
     Self-hosted personal-health-tracking PWA — public API surface for the iOS native client and external ingest.