Fix days-filter in aggregate_model_usage: COALESCE(startTime,'') is invalid SQL (empty-string not a timestamp) — windowed queries always failed to empty

app/main.py

@@ -248,9 +248,9 @@ def aggregate_model_usage(days: int = 0, team_id: str | None = None) -> dict:
     if days and days > 0:
         from datetime import datetime, timedelta, timezone
         cutoff = (datetime.now(timezone.utc) - timedelta(days=days)).strftime(
-            "%Y-%m-%dT%H:%M:%S"
+            "%Y-%m-%d %H:%M:%S"
         )
-        where.append("COALESCE(\"startTime\", '') >= %s")
+        where.append("\"startTime\" >= %s")
         params.append(cutoff)
     if team_id:
         where.append("team_id = %s")