feat(backtest): 参数网格寻优（optimizer + 前端寻优页）

对单个策略的 1-2 个参数做网格搜索，遍历用户指定的取值列表笛卡尔积，
每个组合跑一次回测，按 total_return 排序，返回排名表 + 热力图。

后端：
- ParamGridOptimizer（backtest/optimizer.py）：itertools.product 遍历网格，
  每点 entry.build(params) + BacktestEngine.run(df)，复用同一 DataFrame
- 网格大小上限 200 防组合爆炸，单点失败容错（跳过不中断）
- 2 参数时生成热力图矩阵（x/y 轴取值 + cell 收益率）
- POST /backtest/optimize/run/async 端点（后台任务）
- OptimizeBacktestRequest schema（param_grid 1-2 参数）

前端（/optimize 寻优页）：
- ParamGridPicker：勾选 1-2 个寻优参数，逗号分隔填取值列表
- OptimizeResultTable：网格点排名表（按收益降序，最优高亮）
- OptimizeHeatmap：2 参数热力图（ECharts heatmap，绿→红映射收益）
- 最优点「查看」按钮跳转单标的页用该参数回测

测试：821 passed（+10 寻优器单测 + 3 寻优路由测试）

tests/unit/test_web_backtest.py

@@ -807,3 +807,93 @@ def test_portfolio_backtest_bad_strategy(client, monkeypatch):
             break
         time.sleep(0.05)
     assert final["status"] == "failed"
+
+
+# ---------------------------------------------------------------------------
+# Phase 4: 参数网格寻优路由
+# ---------------------------------------------------------------------------
+
+
+def test_optimize_request_validation():
+    """寻优请求校验：param_grid 非空、至少 1 个数据源。"""
+    from easy_tdx.web.backtest_schemas import OptimizeBacktestRequest
+
+    one_bar = [
+        {
+            "datetime": "2024-01-01",
+            "open": 1,
+            "high": 1,
+            "low": 1,
+            "close": 1,
+            "vol": 1,
+            "amount": 1,
+        }
+    ]
+    req = OptimizeBacktestRequest(
+        strategy="ma_cross",
+        param_grid={"fast": [5, 10], "slow": [20, 30]},
+        ohlcv=one_bar,
+    )
+    assert len(req.param_grid) == 2
+    with pytest.raises(ValueError):
+        OptimizeBacktestRequest(strategy="ma_cross", param_grid={"fast": [5]})  # 缺数据源
+    with pytest.raises(ValueError):
+        OptimizeBacktestRequest(  # param_grid > 2 参数
+            strategy="ma_cross",
+            param_grid={"a": [1], "b": [2], "c": [3]},
+            ohlcv=one_bar,
+        )
+
+
+def test_optimize_endpoint(client, sample_ohlcv):
+    """POST /backtest/optimize/run/async 端到端（内联数据）。"""
+    resp = client.post(
+        "/api/v1/backtest/optimize/run/async",
+        json={
+            "strategy": "ma_cross",
+            "param_grid": {"fast": [5, 10], "slow": [20, 30]},
+            "cash": 100000,
+            "ohlcv": sample_ohlcv,
+        },
+    )
+    assert resp.status_code == 202, resp.text
+    task_id = resp.json()["task_id"]
+
+    final = None
+    for _ in range(200):
+        poll = client.get(f"/api/v1/backtest/tasks/{task_id}")
+        final = poll.json()
+        if final["status"] in ("done", "failed"):
+            break
+        time.sleep(0.05)
+
+    assert final["status"] == "done", final
+    result = final["result"]
+    assert result["strategy"] == "ma_cross"
+    assert result["param_names"] == ["fast", "slow"]
+    assert len(result["results"]) == 4
+    assert result["best"] is not None
+    assert result["heatmap"] is not None
+    assert len(result["heatmap"]["data"]) == 4
+
+
+def test_optimize_single_param_no_heatmap(client, sample_ohlcv):
+    """单参数寻优不应返回热力图。"""
+    resp = client.post(
+        "/api/v1/backtest/optimize/run/async",
+        json={
+            "strategy": "rsi_reversal",
+            "param_grid": {"n": [7, 14, 21]},
+            "ohlcv": sample_ohlcv,
+        },
+    )
+    assert resp.status_code == 202
+    task_id = resp.json()["task_id"]
+    for _ in range(200):
+        poll = client.get(f"/api/v1/backtest/tasks/{task_id}")
+        final = poll.json()
+        if final["status"] in ("done", "failed"):
+            break
+        time.sleep(0.05)
+    assert final["status"] == "done"
+    assert final["result"]["heatmap"] is None