perf: remove redundant COUNT query and use bulk insert for CSV imports

app/routes/main.py

@@ -288,12 +288,9 @@ def prepare_graph_data(readings):
 
 def calculate_progress_badges(user_id, user_tz):
     """Generate badges based on user activity and milestones using optimized queries."""
-    total_readings = Reading.query.filter_by(user_id=user_id).count()
-    if total_readings == 0:
-        return []
-
-    # Fetch only timestamps (highly optimized compared to fetching full objects)
+    # Fetch only timestamps (index-only scan on the composite index)
     timestamps = db.session.query(Reading.timestamp).filter(Reading.user_id == user_id).order_by(Reading.timestamp.desc()).all()
+    total_readings = len(timestamps)
     return _compute_badges(total_readings, timestamps, user_tz)
 
 def _compute_badges(total_readings, timestamps, user_tz, now_local=None):