fix: 上次同步时间转为本地时区显示，修正时区混淆问题

AppConfig 存储 UTC 时间，模板直接输出导致用户在上海(UTC+8)看到错误时刻。
新增 get_last_sync_at_local() 转本地时区，logs_view 采用本地时间显示。

log_storage.py

@@ -797,6 +797,23 @@ def get_last_sync_path() -> str | None:
         return None
 
 
+def get_last_sync_at_local() -> str | None:
+    """Return the last-sync timestamp formatted in local time (not UTC).
+
+    :class:`~app.AppConfig` stores the sync time as an ISO-8601 UTC string
+    (e.g. ``2026-07-16T07:43:36Z``). This converts it to the system's local
+    timezone so the UI shows a human-friendly time to the operator.
+    """
+    ts = get_last_sync_at()
+    if not ts:
+        return None
+    try:
+        dt = datetime.fromisoformat(ts.replace("Z", "+00:00"))
+        return dt.astimezone().strftime("%Y-%m-%d %H:%M:%S")
+    except Exception:
+        return ts
+
+
 def import_full_history(
     path: str,
     instance_id: int = 0,