chore(release): v1.28.18 — Google Health sleep reads its true total

Google re-scores a night after the fact, and the sync re-reads recent nights to
pick that up. The per-segment sleep externalId keyed on a volatile anchor (the
session end instant plus a positional index), so a re-read minted fresh ids and
landed as a SECOND parallel copy of the night instead of overwriting the first —
the night-total then summed both (a real 7h35 night could read as 10h+).

Each segment now keys on a stable identity: the session's own resource id (as the
workout mapper already does) plus the segment's own start, dropping the shifting
end anchor and the positional index. A mere re-classification of a block now
updates in place. And before writing a re-read night, the sync soft-deletes any
superseded rows left in that night's window (bounded to the session's own span,
never a fresh row), so the night collapses to one canonical set.

Nights already stored with duplicates heal as they are re-read within the sync
overlap; scripts/repair-google-health-sleep.ts re-syncs the full history at once
for older nights (dry-run by default, --run to execute).

package.json

@@ -1,6 +1,6 @@
 {
   "name": "healthlog",
-  "version": "1.28.17",
+  "version": "1.28.18",
   "description": "Self-hosted personal-health-tracking PWA with Withings integration, AI insights, and doctor-report PDF export.",
   "license": "PolyForm-Noncommercial-1.0.0",
   "homepage": "https://healthlog.dev",