Merge upstream v1.38.7

Only CHANGELOG.md conflicted: v1.38.7 released while this branch was open,
so the new release heading landed where the branch's [Unreleased] section
sits. The HRV entries stay under [Unreleased] above 1.38.7; everything from
1.38.7 down is upstream's file verbatim.

docs/api/openapi.yaml auto-merged. Upstream's only change there was the
`info.version` bump to 1.38.7, which the merge took while keeping this
branch's DashboardLayoutReadResult, and package.json now reads 1.38.7 to
match — so the merged file should equal a fresh generate. It is a generated
file, though, so confirm with `pnpm openapi:generate` rather than trusting
the three-way merge.

docs/api/openapi.yaml

@@ -1,7 +1,7 @@
 openapi: 3.1.0
 info:
   title: HealthLog API
-  version: 1.38.6
+  version: 1.38.7
   description: >-
     Self-hosted personal-health-tracking PWA — public API surface for the iOS native client and external ingest.