fix(stats): finalize snapshots on the verse-day window

A verse date is a player's local calendar day, spanning D-1 10:00Z
(UTC+14) through D+1 12:00Z (UTC-12). The old UTC end-of-day cutoff both
dropped late-night finishes in negative timezones and could persist a
partial day.

- Scope snapshot loads by the verse date column; use completedBefore only
  to pin an in-progress point-in-time build.
- Gate persistence on isDayClosed (D+1 12:00Z); open days are computed
  live and never written.
- Build the cron snapshot for latestClosedDate instead of EST yesterday,
  and read the same date for the community page.
- Add all-time best single day to snapshot totals.
- Bump PAYLOAD_SCHEMA_VERSION to 4 and extend snapshot/window tests.

statistics-plan.md

@@ -220,10 +220,10 @@ Indexes: `(name, date)`, `(anonymous_id, date)`. **Unique** on `(name, anonymous
 **`user.created_at`** — new timestamp column (see §7).
 
 ### 6.2 Snapshot build
-- **Trigger:** daily cron hits a protected `POST /api/cron/build-stats` (bearer `CRON_SECRET`, same pattern as `/api/send-daily-verse`). It builds yesterday's snapshot and sends the digest.
+- **Trigger:** daily cron hits a protected `POST /api/cron/build-stats` (bearer `CRON_SECRET`, same pattern as `/api/send-daily-verse`). It builds the most recent date whose global data window has closed and sends the digest.
 - **Lazy fallback:** `/admin/stats` load builds a missing snapshot on demand (guarded against races, marked `lazy`).
 - **Backfill:** an admin action/script can reconstruct a date range from raw data (marked `reconstructed`).
-- **Computation cutoff:** only data with `date <= asOfDate` (and `completedAt` before end of that day) — guarantees point-in-time.
+- **Computation cutoff:** data is grouped by the verse `date` (a player's local day), not a UTC 24-hour window. A date is final after `D+1 12:00Z` (UTC-12 has finished the day); until then a build is a non-persisted point-in-time view. Snapshots are only persisted once the window has closed.
 - **Player state (for render-time config):** per player active in the trailing ~180 days, a compact tuple `[anonId, firstDate, lastDate, totalPlays, plays7, plays30, currentStreak]`. Thresholds applied at render time, so changing them re-segments **all history instantly** while the state stays frozen as of that day.
 - **Retention/pruning:** keep all snapshots (small); optionally prune `player_state` older than a configurable horizon later.