feat: stabilize workflow phase 1 foundation

backend/app/domains/rendering/workflow_schema.py

@@ -21,10 +21,22 @@ from pydantic import BaseModel, Field, field_validator, model_validator
 from app.core.process_steps import StepName
 
 
+class WorkflowPosition(BaseModel):
+    x: float
+    y: float
+
+
+class WorkflowNodeUI(BaseModel):
+    type: str | None = None
+    position: WorkflowPosition | None = None
+    label: str | None = None
+
+
 class WorkflowNode(BaseModel):
     id: str
     step: StepName  # validated against the StepName StrEnum
     params: dict = {}
+    ui: WorkflowNodeUI | None = None
 
 
 class WorkflowEdge(BaseModel):
@@ -35,10 +47,15 @@ class WorkflowEdge(BaseModel):
     model_config = {"populate_by_name": True}
 
 
+class WorkflowUI(BaseModel):
+    preset: str | None = None
+
+
 class WorkflowConfig(BaseModel):
     version: int = 1
     nodes: list[WorkflowNode]
     edges: list[WorkflowEdge] = []
+    ui: WorkflowUI | None = None
 
     @field_validator("nodes")
     @classmethod