实现流量控制前馈 + 增益调度（MFC 结构）

按 plan.md 新增三个交付物，全部默认关闭以保持与纯 PID 的 A/B 兼容：

- valve_model.py：阀特性模型 Q_ss = A_eff(x)·P1_abs·F(r)，含 ISO 6358
  椭圆 F(r)、行程/面积互逆插值、单调性校验、JSON 存取。
- identify_valve.py：从 open_loop.py 扫点 CSV 拟合 A_eff 表并输出 JSON。
- 控制器集成：config/flow_control/main/data_logger 新增阀前压读取
  （channel 2）、前馈打底 + PI 修残差、按 P1 增益调度，并记录/绘制前馈项。

新增配置 FEEDFORWARD_ENABLED / GAIN_SCHEDULE_ENABLED 默认 False，
VALVE_MODEL_PATH 默认空，未加载模型时行为与原先纯 PID 完全一致。

data_logger.py

@@ -13,8 +13,12 @@ CSV_FIELDS = (
     "measured_flow_slm",
     "opening_pct",
     "pressure_kpa",
+    "pressure_before_kpa",
     "error_slm",
     "motor_position",
+    "feedforward_pct",
+    "correction_pct",
+    "gain_scale",
     "actual_dt_s",
     "status",
 )
@@ -59,8 +63,14 @@ class FlowRunRecorder:
                 ),
                 "opening_pct": self._format_value(result.opening_pct),
                 "pressure_kpa": self._format_value(result.pressure_kpa),
+                "pressure_before_kpa": self._format_value(
+                    result.pressure_before_kpa
+                ),
                 "error_slm": self._format_value(result.error_slm),
                 "motor_position": self._format_value(result.motor_position),
+                "feedforward_pct": self._format_value(result.feedforward_pct),
+                "correction_pct": self._format_value(result.correction_pct),
+                "gain_scale": self._format_value(result.gain_scale),
                 "actual_dt_s": self._format_value(result.actual_dt_s),
                 "status": result.status,
             }
@@ -93,6 +103,7 @@ class FlowRunRecorder:
         target_flow = []
         measured_flow = []
         opening = []
+        feedforward = []
         pressure = []
 
         with self.csv_path.open("r", newline="", encoding="utf-8-sig") as file:
@@ -103,6 +114,9 @@ class FlowRunRecorder:
                     self._float_or_nan(row["measured_flow_slm"])
                 )
                 opening.append(self._float_or_nan(row["opening_pct"]))
+                feedforward.append(
+                    self._float_or_nan(row.get("feedforward_pct"))
+                )
                 pressure.append(self._float_or_nan(row["pressure_kpa"]))
 
         figure, axes = plt.subplots(
@@ -138,7 +152,18 @@ class FlowRunRecorder:
             opening,
             color="#2E7D32",
             linewidth=1.4,
+            label="Opening",
         )
+        if any(math.isfinite(value) for value in feedforward):
+            axes[1].plot(
+                time_s,
+                feedforward,
+                color="#EF6C00",
+                linewidth=1.2,
+                linestyle="--",
+                label="Feedforward",
+            )
+            axes[1].legend(loc="best")
         axes[1].set_ylabel("Opening (%)")
         axes[1].set_title("Valve opening")
         axes[1].set_ylim(-2, 102)