Topology modelling, editing, and simulation wiring

[bnmajor]

A user creates and edits a named topology, sees it on a read-only graph, and a run uses it.

Goal

Reproduce the checked-in example topology through the UI: 3 switches (A, B, C), 2 terminals each, and 5 directed links - A -> B, B -> A, B -> C, C -> B, C -> A, and no A -> C (A -> C traffic routes through B).

• Component presets are not a part of this step. Every switch field is editable directly on the topology page so this feature can ship without the component model changes.
• terminals should live on the node, not on a preset
• The canvas renders switches only: 3 nodes and 5 links, terminals as a badge/count.
• YAML is generated at launch, not at topology-save
• No latency field and no routing field. FFW has no per-link latency and routing is computed by compute_routes().

Note

This feature will need to write the LP counts into the simulation config YAML, which the simulation feature owns.