perf(data): TickFlow 取数切换 as_dataframe=False 列式直转; 修复除权因子日期 UTC 偏移一天

- 全部 K 线取数点改走 CompactKlineData 列式直转 polars (无 pandas 中转,
  全市场单轮本地转换 ~1.1s → ~0.1s), 时区口径统一 _timestamp_to_beijing_datetime
- 除权因子 trade_date 原取 UTC 日期, 北京零点事件整体早一天 → 转北京墙钟后取日期
- 盘中分钟增量间隔上限 300s → 120s (universe 仅回最新 3 根, 超限必留缺口)

backend/tests/test_minute_refresh.py

@@ -272,12 +272,12 @@ def test_refresh_preferences_defaults_and_clamp(tmp_path, monkeypatch):
     preferences.save({"minute_refresh_interval": 1})
     assert preferences.get_minute_refresh_interval() == 3  # 下限
     preferences.save({"minute_refresh_interval": 999})
-    assert preferences.get_minute_refresh_interval() == 300  # 上限
+    assert preferences.get_minute_refresh_interval() == 120  # 上限
     preferences.save({"minute_refresh_interval": 15})
     assert preferences.get_minute_refresh_interval() == 15
 
 def test_realtime_monitor_config_owns_refresh_keys(tmp_path, monkeypatch):
-    """盘中增量配置归属实时监控端点 (set_realtime_monitor_config), 并 clamp 到 [3,300]。"""
+    """盘中增量配置归属实时监控端点 (set_realtime_monitor_config), 并 clamp 到 [3,120]。"""
     _isolated_prefs(tmp_path, monkeypatch)
     saved = preferences.set_realtime_monitor_config({
         "minute_refresh_enabled": True,
@@ -286,7 +286,7 @@ def test_realtime_monitor_config_owns_refresh_keys(tmp_path, monkeypatch):
     assert saved["minute_refresh_enabled"] is True
     assert saved["minute_refresh_interval"] == 3
     saved = preferences.set_realtime_monitor_config({"minute_refresh_interval": 400})
-    assert saved["minute_refresh_interval"] == 300
+    assert saved["minute_refresh_interval"] == 120
     saved = preferences.set_realtime_monitor_config({"minute_refresh_interval": 6})
     assert saved["minute_refresh_interval"] == 6