Fix wellness sync crash on None body battery levels

Guard bb variable scope and filter None entries from bodyBatteryValuesArray
before subtraction in _compute_body_battery_hires.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/services/garmin_connect_sync.py

@@ -252,6 +252,7 @@ def sync_wellness(garmin, user_id: int, since: Optional[datetime], db,
                 _set(row, "weight_kg", round(bwf / 1000 if bwf > 300 else bwf, 2))
 
         # Body battery — store summary + fine-grained timeline
+        bb = None
         if bb_raw:
             bb = _parse_body_battery(bb_raw, day_str)
             if bb:
@@ -374,7 +375,11 @@ def _compute_body_battery_hires(bb_values, intraday_hr):
     if not bb_values or not intraday_hr or len(bb_values) < 2:
         return None
 
-    bb  = sorted(bb_values,  key=lambda x: x[0])
+    # Drop entries with None timestamp or level — raw API data can have gaps
+    bb  = sorted([v for v in bb_values if v[0] is not None and v[1] is not None],
+                 key=lambda x: x[0])
+    if len(bb) < 2:
+        return None
     hr  = sorted(intraday_hr, key=lambda x: x[0])
 
     hr_vals = [bpm for _, bpm in hr if bpm is not None and bpm > 0]