refactor: 提取 hex_to_rgba 函数规范颜色透明度处理

将图表 fill 颜色的硬编码十六进制拼接替换为 hex_to_rgba
  辅助函数调用，使颜色转换逻辑更清晰、可维护。

app.py

@@ -8,6 +8,15 @@ from plotly.subplots import make_subplots
 
 from simulator import run_wofost, run_multi_crop, list_available_crops, CROP_META
 
+
+def hex_to_rgba(hex_color: str, alpha: float = 0.1) -> str:
+    hex_color = hex_color.lstrip("#")
+    r = int(hex_color[0:2], 16)
+    g = int(hex_color[2:4], 16)
+    b = int(hex_color[4:6], 16)
+    return f"rgba({r}, {g}, {b}, {alpha})"
+
+
 # ─── Page Config ────────────────────────────────────────────────────────────
 st.set_page_config(
     page_title="麦麦智农",
@@ -274,7 +283,7 @@ with chart_left:
             mode="lines",
             line=dict(color=crop_info["color"], width=2.5),
             fill="tozeroy",
-            fillcolor=crop_info["color"] + "1A",
+            fillcolor=hex_to_rgba(crop_info["color"], 0.1),
             name="LAI",
         ))
         # 添加生育期标记