feat(sync): 每小时后台自动同步 + 手动拉取最新接口

- services/scheduler.py：通过 job_locks 表跨 worker 抢占，
  gunicorn 多进程下一个周期只跑一次；claim 超时 30 分钟自动释放，
  避免 worker 中途挂掉把任务永久卡死
- POST /api/garmin/sync-latest：同步执行，窗口 clamp 到 1..7 天
- GET  /api/garmin/auto-sync：返回上次/下次运行时间
- db.py：注释里的分号会被 SCHEMA.split(";") 截断，改为先剥注释再切分

19 项调度器测试，全量 324 项通过

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

backend/routes/garmin.py

@@ -5,6 +5,7 @@ from auth import require_auth
 from db import query_one
 from services import garmin as garmin_svc
 from services import garmin_auth
+from services import scheduler
 
 bp = Blueprint("garmin", __name__)
 
@@ -119,3 +120,31 @@ def cancel_login():
 @require_auth
 def status():
     return jsonify(garmin_svc.get_sync_status(g.user_id))
+
+
+@bp.route("/sync-latest", methods=["POST"])
+@require_auth
+def sync_latest():
+    """Pull just the last couple of days.
+
+    Separate from /sync because it is fast enough to wait for (a few seconds
+    rather than minutes), so the UI can report the result directly instead of
+    handing back a job to poll.
+    """
+    if not garmin_svc.has_token(g.user_id):
+        return jsonify({"error": "尚未绑定 Garmin 账号"}), 400
+
+    days = request.get_json(silent=True) or {}
+    try:
+        window = max(1, min(int(days.get("days", scheduler.SYNC_DAYS)), 7))
+    except (TypeError, ValueError):
+        window = scheduler.SYNC_DAYS
+
+    return jsonify(garmin_svc.sync_data(g.user_id, {}, days=window))
+
+
+@bp.route("/auto-sync", methods=["GET"])
+@require_auth
+def auto_sync_status():
+    """When the scheduler last ran and when it runs next."""
+    return jsonify(scheduler.status())