lb-autoheal: take the daily history snapshot under the leaderboard lock

_sm_lb_keep_history_fresh() iterated the 1.6M-row players dict via
_sm_leaderboard_snapshot_daily WITHOUT the lock, so a concurrent ingest
could raise "dict changed size during iteration" and skip that day's
snapshot. Hold _SM_LEADERBOARD_LOCK across the daily snapshot (the hourly
one still runs outside it -- it takes the lock itself). Cheap: the daily
does real work only once/day, a file-exists check otherwise.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app.py

@@ -12651,10 +12651,10 @@ def _sm_lb_keep_history_fresh():
     snapshots here so A always holds fresh bootstrap history. Once/hour + once/day of real work;
     a file-exists check otherwise."""
     try:
-        _sm_leaderboard_snapshot_hourly()
+        _sm_leaderboard_snapshot_hourly()   # acquires the lock itself -> call it OUTSIDE the lock
         with _SM_LEADERBOARD_LOCK:
             state = _sm_leaderboard_load_unlocked()
-        _sm_leaderboard_snapshot_daily(state)
+            _sm_leaderboard_snapshot_daily(state)   # iterate players under the lock (no mid-iter mutation)
     except Exception as exc:  # noqa: BLE001
         print(f"[lb-autoheal] snapshot keep-fresh: {type(exc).__name__}: {str(exc)[:120]}")