Model nodes can be deleted again

Deleting a node whose id contains a slash failed with "Node not found" — about a node the very same tools could open, read and edit. The misleading part was the error: "not found" sends you looking for a missing node or a permission problem, and neither was the matter.

This was not a corner case. Every language-model node is named by its provider's wire id — z-ai/glm-5.3, anthropic/claude-opus-5, openai/gpt-5.2 — so no model node could be removed through the API or the assistant's tools at all. Retiring a model, an ordinary operator action, had no programmatic route left; only the node's own Delete page still worked.

The storage layer had been taking a node's path apart by splitting it at the last slash, which puts half of a vendor-prefixed id into the wrong place and matches no stored row. Every read, existence check, batch read and delete now addresses a node by its full path instead, so a slash in an id is simply part of the id — the way create, read and edit have always treated it.

Version history for such nodes is fixed by the same change.