perf: bound public activity aggregation

apps/api/app/activity.py

@@ -10,6 +10,8 @@ from sqlalchemy.orm import Session, joinedload
 from .models import CatchReport, ModerationStatus
 from .schemas import ActivityOut
 
+MAX_ACTIVITY_FACTS = 10_000
+
 
 def activity_rows(
     session: Session,
@@ -33,6 +35,8 @@ def activity_rows(
             CatchReport.spot_id.is_not(None),
             CatchReport.reported_at >= now - timedelta(hours=hours),
         )
+        .order_by(CatchReport.reported_at.desc(), CatchReport.id.desc())
+        .limit(MAX_ACTIVITY_FACTS)
     )
     if waterbody:
         query = query.where(CatchReport.waterbody.has(slug=waterbody))