feat(inspect): sibling FreeCAD and Blender inspect, BYO CAD MCP

[av151318]

What changed

Sibling inspect panels next to KiCad: FreeCAD and Blender.

• KiCad inner tabs stay KiCad-only: Schematic, PCB, 3D, Gerbers, STEP.
• FreeCAD shows saved enclosure solids (GLB/STEP).
• Blender keeps a 3D mesh visible and a separate Render picker for other saved render files in the workspace. Picking a render does not replace the 3D view.
• Inspect rereads saved files. It does not launch those apps. It does not speak MCP.
• Switching panels remounts so chrome cannot leak.

Why

Backplane already inspects electronics in the right panel. Enclosure solids and product renders are the same class of saved file. Nesting them inside KiCad made the tools look like KiCad tabs. Siblings keep KiCad's viewer KiCad-only.

BYO MCP

Driving CAD is bring-your-own MCP on the agent, the same way you can drive KiCad with your own server instead of stock Backplane KiCad. This PR does not vendor an MCP.

Servers used to prove it (examples, not dependencies):

• KiCad: https://github.com/mixelpixx/KiCAD-MCP-Server
• FreeCAD: https://github.com/neka-nat/freecad-mcp
• Blender: https://github.com/ahujasid/blender-mcp

Any equivalent can replace them. Keep the inspect pointers in .backplane.json. Same text is in docs/user/kicad.md and a comment on apps/web/src/kicad/cadInspect.ts.

CONTRIBUTING

• One concern: inspect overlay. 18 files, +991 / −50 vs main.
• User guide updated. No extra docs catalog.
• Did not mix generate/place/route/DRC.

This is still a feature, not a bugfix. Fine if you close it.

CONTRIBUTING says Ideas first. Discussions are not enabled on this repository, so the idea is stated here instead of a separate Ideas post.

UI

Add menu (KiCad / FreeCAD / Blender as siblings):

KiCad panel, KiCad-only inner tabs:

FreeCAD sibling, enclosure solid:

Blender sibling, 3D plus separate Render picker:

Test plan

• cadInspect + rightPanelStore unit tests
• KiCadProject + KiCadModel tests
• KiCad panel inner tabs stay KiCad-only
• FreeCAD and Blender panels do not show that KiCad tablist
• Reviewer: open KiCad, FreeCAD, and Blender from the add menu. Blender keeps 3D while Render switches between other render files in the workspace.

[av151318]

Sorry for the earlier noise. I pushed WIP into this PR instead of keeping a draft. CONTRIBUTING already said discuss first and keep it small. I own that.

This update is the local pass that tries to fit the bar: sibling inspect, KiCad tabs KiCad-only, Blender 3D plus a Render picker, 991 insertions. Inspect is view-only. Chat plus BYO MCP is what edits. The three servers I used are listed in the description as examples, not dependencies.

CONTRIBUTING points Ideas discussions first. Discussions are not enabled on this repo, so the idea is in the description above.