fix(measurements): stop the derived resting mint from suppressing itself

The dense-intraday fold tombstones the raw heart-rate readings a proxy
account's resting figure is derived from, and mints one derived
RESTING_HEART_RATE row per folded day to carry the figure forward. The
mint is skipped for accounts that already hold native resting rows,
because the read resolver ignores the proxy for them.

The probe behind that skip matched every source, including the COMPUTED
rows the mint itself writes. From the second run onward it therefore
reported native resting data for every proxy account, skipped the mint,
and let the fold delete that day's raw readings anyway - losing the
resting figure permanently, once per run.

Scope the probe to non-computed sources. Adds a regression test that
reproduces the second-run state and fails on the previous code.

chore(release): v1.30.16

docs/api/openapi.yaml

@@ -1,7 +1,7 @@
 openapi: 3.1.0
 info:
   title: HealthLog API
-  version: 1.30.15
+  version: 1.30.16
   description: >-
     Self-hosted personal-health-tracking PWA — public API surface for the iOS native client and external ingest.