fix: attach MCP-created nodes/edges to a design (#225)

create_node/create_edge persisted rows with design_id=null when the
client omitted it (the MCP write tools), so they existed in the DB but
never rendered on the canvas until a container restart reconciled them.
Both routes now fall back to the first design, matching bulk-approve.

Also fix MCP resource reads (homelable://canvas, homelable://edges):
the framework passes a pydantic AnyUrl, not a str, which raised
"'AnyUrl' object has no attribute 'startswith'". Coerce to str.

EdgeResponse now exposes design_id for symmetry with NodeResponse.

ha-relevant: no

mcp/app/resources.py

@@ -21,6 +21,10 @@ ROUTES = {
 
 
 async def read_resource(uri: str) -> list[TextContent]:
+    # The MCP framework hands us a pydantic AnyUrl, not a plain str, so string
+    # ops like .startswith / dict lookups blow up with
+    # "'AnyUrl' object has no attribute 'startswith'". Coerce to str first.
+    uri = str(uri)
     if uri.startswith("homelable://nodes/") and uri != "homelable://nodes/":
         node_id = uri.split("/")[-1]
         data = await backend.get(f"/api/v1/nodes/{node_id}")