feat(selection): show gold brick chart below volume in stock detail panel

Add an optional brick_chart series to the selection chart API, computed
from the shared gold-brick formula when strategy=gold_brick, and render
a fourth grid with red/green brick bars between the volume and J grids.

zhixing-server/tests/test_selection_http.py

@@ -109,10 +109,15 @@ class FakeChartService:
 
     def __init__(self) -> None:
         self.mode = "ok"
-        self.request: tuple[str, date] | None = None
+        self.request: tuple[str, date, bool] | None = None
 
-    def execute(self, ts_code: str, target_trade_date: date) -> SelectionChart:
-        self.request = (ts_code, target_trade_date)
+    def execute(
+        self,
+        ts_code: str,
+        target_trade_date: date,
+        include_brick_chart: bool = False,
+    ) -> SelectionChart:
+        self.request = (ts_code, target_trade_date, include_brick_chart)
         if self.mode == "missing":
             raise SelectionChartNotFound("chart unavailable")
         if self.mode == "storage_error":
@@ -135,6 +140,7 @@ class FakeChartService:
                     j=60.0,
                     trend_white=10.2,
                     trend_yellow=10.4,
+                    brick_chart=5.0 if include_brick_chart else None,
                 ),
             ),
         )
@@ -436,7 +442,7 @@ def test_chart_returns_bounded_qfq_contract() -> None:
     )
 
     assert response.status_code == 200
-    assert chart_service.request == ("000001.SZ", TARGET)
+    assert chart_service.request == ("000001.SZ", TARGET, False)
     assert response.json() == {
         "ts_code": "000001.SZ",
         "name": "平安银行",
@@ -455,11 +461,25 @@ def test_chart_returns_bounded_qfq_contract() -> None:
                 "j": 60.0,
                 "trend_white": 10.2,
                 "trend_yellow": 10.4,
+                "brick_chart": None,
             }
         ],
     }
 
 
+def test_chart_requests_brick_series_for_gold_brick_strategy() -> None:
+    chart_service = FakeChartService()
+
+    response = _client(FakeSelectionService(), chart_service).get(
+        "/api/v1/selection/stocks/000001.SZ/chart",
+        params={"target_trade_date": "2026-08-08", "strategy": "gold_brick"},
+    )
+
+    assert response.status_code == 200
+    assert chart_service.request == ("000001.SZ", TARGET, True)
+    assert response.json()["points"][0]["brick_chart"] == 5.0
+
+
 @pytest.mark.parametrize(
     ("mode", "status_code", "error_code"),
     [