fix(measurements): report folded provider heart rate to the change feed

The dense fold deleted Google Health and Oura samples outright, on the
reasoning that no client pulls them. The change feed serves every
source, so a client mirroring it kept those samples next to the hourly
means with nothing to tell it they were gone.

The nightly increment of a server-pulled source is tombstoned again: the
feed reports each sample and the tombstone cleanup purges them after the
retention. A backlog day, such as an account's first fold, is still
deleted outright, and the account's delta cursors expire instead, since
tombstoning millions of rows would undo the point of the fold. The
compaction-tombstone class leaves these sources out, so the feed, the
backlog purge and the restore treat their tombstones like any deletion.
Apple Health and Health Connect are unchanged.

src/__tests__/baselines/source-function-lines.json

@@ -1,7 +1,7 @@
 {
   "$comment": "Production functions over 200 lines, keyed \"file :: name\", and their length. Maintained by src/__tests__/source-size-ratchet.test.ts.",
   "count": 346,
-  "total": 112215,
+  "total": 112219,
   "entries": {
     "app/achievements/page.tsx :: AchievementsPage": 206,
     "app/api/admin/backups/upload/route.ts :: apiHandler(arg)": 286,
@@ -319,9 +319,9 @@
     "lib/labs/biomarker-merge.ts :: runMerge": 254,
     "lib/measurements/consolidate-daily-mean.ts :: consolidateDailyMean": 278,
     "lib/measurements/consolidate-legacy-steps.ts :: consolidateLegacySteps": 263,
-    "lib/measurements/dense-intraday-retention.ts :: runDenseIntradayRetention": 537,
-    "lib/measurements/dense-intraday-retention.ts :: runDenseIntradayRetention > walkSource": 447,
-    "lib/measurements/dense-intraday-retention.ts :: runDenseIntradayRetention > walkSource > writeDay": 373,
+    "lib/measurements/dense-intraday-retention.ts :: runDenseIntradayRetention": 539,
+    "lib/measurements/dense-intraday-retention.ts :: runDenseIntradayRetention > walkSource": 448,
+    "lib/measurements/dense-intraday-retention.ts :: runDenseIntradayRetention > walkSource > writeDay": 374,
     "lib/measurements/dense-intraday-retention.ts :: runDenseIntradayRetention > walkSource > writeDay > foldOnce": 212,
     "lib/measurements/drain-per-sample-cumulative.ts :: drainPerSampleCumulative": 344,
     "lib/measurements/drain-per-sample-cumulative.ts :: drainPerSampleCumulative > writeDay": 205,