fix: anchor hedge contribution bars at zero

app/pages/hedge.py

@@ -33,19 +33,8 @@ def _cost_benefit_options(metrics: dict) -> dict:
 
 def _waterfall_options(metrics: dict) -> dict:
     steps = metrics["waterfall_steps"]
-    running = 0.0
-    base: list[float] = []
     values: list[dict[str, object]] = []
-    for index, (label, amount) in enumerate(steps):
-        if index == 0:
-            base.append(0)
-            running = amount
-        elif index == len(steps) - 1:
-            base.append(0)
-        else:
-            base.append(running)
-            running += amount
-
+    for label, amount in steps:
         color = "#0ea5e9" if label == "Net equity" else ("#22c55e" if amount >= 0 else "#ef4444")
         values.append({"value": amount, "itemStyle": {"color": color}})
 
@@ -56,14 +45,6 @@ def _waterfall_options(metrics: dict) -> dict:
         "series": [
             {
                 "type": "bar",
-                "stack": "total",
-                "data": base,
-                "itemStyle": {"color": "rgba(0,0,0,0)"},
-                "tooltip": {"show": False},
-            },
-            {
-                "type": "bar",
-                "stack": "total",
                 "data": values,
             },
         ],