fix(sync): rollup-day month check lands in the wrong month at negative UTC offsets

rollup_day is a local epoch day, but the copy-vs-recompute guard read its
month back via day * 86400 (UTC midnight), which resolves to the previous
civil month for the 1st of a month anywhere west of UTC. Anchor at local
noon (+43200) instead. Pre-existing on main, surfaced by CodeRabbit review.

changes/sync-monthly-rollup-timezone.md

@@ -0,0 +1,4 @@
+type: fixed
+area: sync
+
+- Fixed stats sync copying a remote daily rollup that should have been recomputed when the day was the 1st of a month and the machine was on a negative UTC offset (the Americas), which could leave that day's totals wrong after a sync. The rollup day is now read back at local noon instead of UTC midnight, so it always resolves to the correct civil month.

src/core/services/stats-sync/merge-rollups.ts

@@ -193,10 +193,13 @@ export function copyRemoteOnlyRollups(
   const localMonthSessions = local.query(
     `SELECT 1 FROM imm_sessions WHERE video_id = ? AND ${LOCAL_MONTH_EXPR} = ? LIMIT 1`,
   );
+  // rollup_day is a *local* epoch day, so anchor it at local noon (+43200)
+  // before reading its month back: plain UTC midnight lands in the previous
+  // civil month for the 1st of a month at any negative UTC offset.
   const localMonthSessionsForDay = local.query(
     `SELECT 1 FROM imm_sessions
      WHERE video_id = ?
-       AND ${LOCAL_MONTH_EXPR} = CAST(strftime('%Y%m', CAST(? AS INTEGER) * 86400, 'unixepoch', 'localtime') AS INTEGER)
+       AND ${LOCAL_MONTH_EXPR} = CAST(strftime('%Y%m', CAST(? AS INTEGER) * 86400 + 43200, 'unixepoch', 'localtime') AS INTEGER)
      LIMIT 1`,
   );
   const insertDaily = local.query(