Each node can now choose its own model

A model picker now sits on the node. Search the catalogue, see models grouped by provider with their context window and a badge marking the fast and the thinking variants, and set one on the node you are working on.

A node without a model of its own inherits from the nearest ancestor that has one, so setting a model on the head of a branch sets it for the branch. That is what makes a side by side comparison cheap. Branch the same question twice, put a different model on each branch, and read the two answers next to each other.

The catalogue itself now comes from OpenRouter, so the list of available models stays current without a code change.

Open a map and set a model on a node.