Fix avg_hr_day: remove dead averageHeartRate lookup; add max_hr_day from UDS export

garmin.get_stats() never returns averageHeartRate — avg_hr_day is only computable
from intraday HR which Garmin's API only serves for recent dates (~90-120 days).
The dead lookup gave false confidence that historical backfill would work.

Also populate max_hr_day from the Garmin export's UDS daily summaries (maxHeartRate
field is present for the full history), so historical max HR is available after
re-importing the export.

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

backend/app/workers/tasks.py

@@ -422,12 +422,13 @@ def process_garmin_health_zip(zip_path: str, user_id: int):
     from sqlalchemy import text
 
     INSERT_SQL = text("""
-        INSERT INTO health_metrics (user_id, date, resting_hr, steps,
+        INSERT INTO health_metrics (user_id, date, resting_hr, max_hr_day, steps,
             floors_climbed, active_calories, total_calories, avg_stress, spo2_avg)
-        VALUES (:user_id, :date, :resting_hr, :steps,
+        VALUES (:user_id, :date, :resting_hr, :max_hr_day, :steps,
             :floors, :active_cal, :total_cal, :stress, :spo2)
         ON CONFLICT (user_id, date) DO UPDATE SET
             resting_hr      = COALESCE(EXCLUDED.resting_hr, health_metrics.resting_hr),
+            max_hr_day      = COALESCE(EXCLUDED.max_hr_day, health_metrics.max_hr_day),
             steps           = COALESCE(EXCLUDED.steps, health_metrics.steps),
             floors_climbed  = COALESCE(EXCLUDED.floors_climbed, health_metrics.floors_climbed),
             active_calories = COALESCE(EXCLUDED.active_calories, health_metrics.active_calories),
@@ -463,6 +464,7 @@ def process_garmin_health_zip(zip_path: str, user_id: int):
         db.execute(INSERT_SQL, {
             "user_id": user_id, "date": date_dt,
             "resting_hr": item.get("restingHeartRate"),
+            "max_hr_day": item.get("maxHeartRate"),
             "steps": item.get("totalSteps"),
             "floors": _floors_from_item(item),
             "active_cal": item.get("activeKilocalories"),