Fix VO2 max extraction — use fitnessage API not daily stats

get_stats() does not include VO2 max. Switch to get_fitnessage_data()
which hits /fitnessage-service/fitnessage and returns the current VO2
max estimate and fitness age. Called once per sync (today only) since
VO2 max is a slow-changing metric; the frontend carry-forward shows it
on older days. Remove the incorrect stats.get() attempt from _parse_day.

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

backend/app/services/garmin_connect_sync.py

@@ -325,6 +325,31 @@ def sync_wellness(garmin, user_id: int, since: Optional[datetime], db,
             logger.warning("Failed to upsert health_metrics for %s: %s", day_str, exc)
             db.rollback()
 
+    # Fetch current VO2 max and fitness age once (slow-changing — only update today's row)
+    today_str = date.today().isoformat()
+    fa_data = _safe(garmin.get_fitnessage_data, today_str)
+    if fa_data:
+        vo2 = (fa_data.get("vo2Max")
+               or fa_data.get("vo2MaxPreciseValue")
+               or fa_data.get("biometricProfile", {}).get("vo2Max"))
+        fa  = fa_data.get("chronologicalAge") or fa_data.get("fitnessAge")
+        if vo2 and float(vo2) > 0:
+            try:
+                fa_row = {"vo2max": float(vo2)}
+                if fa:
+                    fa_row["fitness_age"] = int(fa)
+                fa_cols = list(fa_row.keys())
+                db.execute(text(f"""
+                    INSERT INTO health_metrics (user_id, date, {", ".join(fa_cols)})
+                    VALUES (:user_id, :day, {", ".join(f":{c}" for c in fa_cols)})
+                    ON CONFLICT (user_id, date) DO UPDATE SET
+                    {", ".join(f"{c} = EXCLUDED.{c}" for c in fa_cols)}
+                """), {"user_id": user_id, "day": today_str, **fa_row})
+                db.commit()
+            except Exception as exc:
+                logger.warning("Failed to upsert VO2 max: %s", exc)
+                db.rollback()
+
     return processed
 
 
@@ -469,9 +494,6 @@ def _parse_day(stats, sleep_data, hrv_data) -> dict:
         _set(row, "active_calories", active)
         if active and bmr:
             _set(row, "total_calories", float(active) + float(bmr))
-        vo2 = stats.get("vo2MaxPreciseValue") or stats.get("vo2Max")
-        if vo2 and float(vo2) > 0:
-            _set(row, "vo2max", float(vo2))
 
     if sleep_data:
         dto = sleep_data.get("dailySleepDTO") or sleep_data