reconcile: fold in the outstanding hardening and data-integrity fixes

Merge the eight reviewed audit fixes that were cut a week ago and never
landed. Main has moved on since, so each fix was re-checked against the
current tree and each of the five conflicts resolved by understanding
both sides.

Kept, still open on main:
- Proxy early exits now carry the transport security header subset via a
  shared helper. Reconciled with main's /api/health worker-only carve-out.
- Batch measurement ingest bounds the entry instant so a future-dated row
  can no longer win "latest reading" or poison the rollup buckets.
- Web Push dials through the pinned safeFetch dispatcher with
  requirePublicHost, closing the last user-controlled-host egress.
- Mood bulk upsert and its tag/factor links run in one transaction, so a
  rejected rating rolls the mood row back instead of leaving a tagless row.
- Full backup carries NutrientIntakeDay with its unit and source. Folded
  into main's portable-export / disaster-recovery split.
- Live daily-series fallback restores the min/max spread band the tiered
  read already emitted.
- Coach stream aborts its in-flight reader on unmount and resets send state
  on a conversation switch.
- Manual water writes share the day-bound helper, nutrient add clamps after
  the increment, and the thiamin cap drops to a real supplement ceiling.
- Compliance point window widens symmetrically instead of wrapping overnight.
- Oura, Polar and Fitbit token helpers classify an empty or non-JSON 2xx
  body as a handled transient error.
- WebAuthn relying-party fallback to localhost is gated to development.
- Chart-token strip list is derived from the allowlist and pinned by a test.
- Regression tests pin the snapshot-cache tenant key, the GlitchTip
  path-secret redaction and the Withings credentials delete.

Superseded by main, tests re-pointed at the current shape:
- The intake CSV import was rewritten on main to run through a background
  job with a single-active-job admission gate. The future-date bound is
  re-applied at request validation and the per-user limiter is kept for
  parity with the bulk twin; the old synchronous-write test is replaced.

src/lib/validations/nutrients.ts

@@ -51,7 +51,7 @@ export const nutrientBatchSchema = z
   .meta({
     id: "NutrientBatchRequest",
     description:
-      "Bulk day-total upsert, max 500 entries. Upsert key is (day, nutrient); a re-post replaces the stored total (last-writer-wins day-total contract).",
+      "Bulk day-total upsert, max 500 entries. Upsert key is the composite primary key (userId, day, nutrient, source); this route always writes the APPLE_HEALTH source row, so a manual water entry is never clobbered. A re-post replaces the stored total (last-writer-wins day-total contract).",
   });
 
 /** Per-entry outcome — a re-post is by definition an update, never a duplicate. */