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.

tests/stats-signals.test.ts

@@ -41,7 +41,7 @@ function makePayload(overrides: {
 			segmentMix: []
 		},
 		growth: { lifecycleFunnel: [], signups: [] },
-		totals: { completions: 0, players: 0, yesterdayCompletions: 0, yesterdayAvgGuesses: null },
+		totals: { completions: 0, players: 0, yesterdayCompletions: 0, yesterdayAvgGuesses: null, bestDay: null },
 		verseMix: {
 			coverage: [],
 			testamentMix: [],