fix: persist edge animation mode (None/Snake/Flow) end-to-end

- canvasStore.onConnect: include animated in edge data object (was silently dropped)
- Backend schemas: normalize animated bool/int to string ('none'/'snake'/'flow') via field_validator
- ORM model: change animated column from Boolean to String
- DB migration: convert existing 0/1 boolean rows to 'none'/'snake' strings

backend/app/schemas/canvas.py

@@ -1,9 +1,10 @@
 from typing import Any
 
-from pydantic import BaseModel
+from pydantic import BaseModel, field_validator
 
 from app.schemas.edges import EdgeResponse
 from app.schemas.nodes import NodeResponse
+from app.schemas.utils import normalize_animated
 
 
 class NodeSave(BaseModel):
@@ -44,10 +45,15 @@ class EdgeSave(BaseModel):
     speed: str | None = None
     custom_color: str | None = None
     path_style: str | None = None
-    animated: bool = False
+    animated: str = 'none'
     source_handle: str | None = None
     target_handle: str | None = None
 
+    @field_validator('animated', mode='before')
+    @classmethod
+    def validate_animated(cls, v: object) -> str:
+        return normalize_animated(v)
+
 
 class CanvasSaveRequest(BaseModel):
     nodes: list[NodeSave] = []