统一组件图标布局并完善选择吸附交互

app/main.py

@@ -139,6 +139,8 @@ class ReactFlowSimulationConfig(BaseModel):
 class ReactFlowProjectPayload(BaseModel):
     name: str = "untitled"
     mediumReferenceVersion: Literal[1] | None = None
+    # 仅用于前端展示布局迁移；求解器和 System XML 不读取该字段。
+    presentationLayoutVersion: Literal[1] | None = None
     # Missing/None is reserved for projects written before canonical AMESim
     # option codes were introduced. Every current writer emits version 1.
     amesimParameterEncodingVersion: Literal[1] | None = Field(