feat：新增物料

app/schemas/screen.py

@@ -1,6 +1,6 @@
 """大屏公共结构；组件属性、事件与数据源配置保持开放"""
 
-from typing import Annotated, Self
+from typing import Annotated, Literal, Self
 
 from pydantic import Field, model_validator
 
@@ -13,6 +13,13 @@ PositiveNumber = Annotated[Number, Field(gt=0)]
 class Canvas(ExtensibleModel):
     width: PositiveNumber
     height: PositiveNumber
+    theme: Literal["light", "dark"] | None = Field(
+        default=None,
+        description="画布主题：组件里没单独设置的文字、坐标轴、分隔线、卡片底等颜色按主题取；旧大屏没有时前端按背景色推断",
+    )
+    backgroundColor: str | None = Field(
+        default=None, description="画布背景色；为 null 时用主题的背景色"
+    )
 
 
 class Layout(ExtensibleModel):