Fail routing on validation issue

[james1236]

Routing can currently pass with modules overlapping, and other validation issues

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If the routing thread ends for any other reason (e.g no modules to route), there's also no error message, so the front-end just keeps checking for progress

[mac-aron]

Frontend should validate the layout, and look at:

• module overlaps,
• modules extending to the board edge,
• board and module margins.

Backend should validate the design on the electrical level:

• module compatability and net names,
• max number of modules/PCB dimensions (as per fabricator capabilities),
• missing brain,
• general situations where the boards will be generated non-functional.

To enable this, let's add backendDesignRules to each module JSON file.

[james1236]

The backend should also validate gerber keep out zone overlaps, rather than relying solely on the frontend.

If the bus widths are needed for validation (e.g. board/module margins), they should be calculated by the backend and sent in a response to the frontend. Otherwise the frontend needs to know about:

• Nets (and how they're changed by flashing pairs)
• Trace width/seperation from fab house capabilities (not yet implemented)
• Predict routing decisions (e.g. like which board layer a net uses)

Right now the frontend has no knowledge of routing. Adding these dependencies would make it more fragile, introduce duplicated logic between frontend and backend, and complicate any future improvements like dynamic layer selection during routing.