Update node properties in place

## Context

Parent: #6897 — FE MQTT Migration

Migrate the `custom:update-node` action from HTTP to MQTT transport. This action allows the Expert to programmatically update node properties without removing and re-adding nodes.

Note from refinement: "These will not be 'bottleneck' — check out the definitions/docs, this is essential."

## Estimate

1h

## Acceptance Criteria

- [ ] Expert can update node properties via MQTT message
- [ ] Node visual state updates in the editor after property change
- [ ] Handles cascading property effects (e.g., changing MQTT version affects available options)