fix(documents): store stated dates at noon UTC

A report's stated date, a document's filing date and the date a committed
lab reading or condition carries were written as UTC midnight, which is
the previous evening west of UTC: a reading dated the 1st showed on the
31st. Date-only values are now stored at noon UTC through one helper in
the time zone module, the convention the lab scan and the cycle engine
already use. Rows written at midnight still read back to the same date.
A document uploaded without a date files under the uploader's own day
rather than the UTC one.

src/lib/documents/commit.ts

@@ -39,6 +39,7 @@ import type {
   MedicationStatementFactData,
   ObservationFactData,
 } from "@/lib/validations/inbound-documents";
+import { dateOnlyAtNoonUtc, isDateOnlyKey } from "@/lib/tz/date-only";
 
 /** A per-fact commit failure the caller maps to a per-fact 422 entry. */
 export class FactCommitError extends Error {
@@ -55,11 +56,13 @@ export interface CommittedRecordRef {
   recordId: string;
 }
 
-/** Parse a stated YYYY-MM-DD into a UTC instant, or fall back to now. */
+/**
+ * A stated YYYY-MM-DD as the instant a date-only value is stored at (noon
+ * UTC), or now when the document states none. UTC midnight read back as the
+ * previous day anywhere west of UTC.
+ */
 function statedDateOrNow(date: string | null): Date {
-  if (date && /^\d{4}-\d{2}-\d{2}$/u.test(date)) {
-    return new Date(`${date}T00:00:00.000Z`);
-  }
+  if (date && isDateOnlyKey(date)) return dateOnlyAtNoonUtc(date);
   return new Date();
 }