Run the kernel as WebAssembly in the Linux CI (#412)

[dsn27]

Part of #412 (step 9, verification).

Base: this PR targets integration/issue-412, because it needs both the font service (#466 → #472) and the picture and page setup changes (#473, #474), which are only combined there. Its own diff is just the smoke test. Retarget it to master once those PRs are merged.

Why

The goal of #412 is that CADability runs in the browser. So far that was argued, not shown. This PR runs CADability.dll in the browser runtime of .NET (WebAssembly, under Node.js) in every Linux CI run.

What

tests/CADability.WasmSmoke is a .NET 10 WebAssembly program (Microsoft.NET.Sdk.WebAssembly). It references CADability.csproj and runs 13 checks, without a frame and without GDI+:

1. register a font from bytes; there are no system fonts in the browser
2. create a project
3. make a box minus a cylinder and check the volume
4. measure a text and get its glyph outlines
5. create a picture from PNG bytes
6. paint the model through RecordingPaintTo3D, an IPaintTo3D of its own that replays display lists, and check the painted extent
7. JSON round trip
8. open a 1.x file with pictures
9. open a 1.x file with page settings
10. open Volumes.cdb.json
11. import a STEP file
12. export DXF and STL, and read the DXF back
13. run the finalizers

The exit code is the number of failed checks. A new step in linux-ci.yml builds the program and runs it with node, which is preinstalled on the runner.

Result

Kernel	Passed	Failed
master (checks adapted to the old API)	6	7: PlatformNotSupportedException from System.Drawing.Common for text, picture and finalizers, and failures that follow from them
integration/issue-412	13	0

What this shows for the plan

• Implementing IPaintTo3D works in the browser. RecordingPaintTo3D implements the interface unchanged, including PrepareBitmap(Bitmap) and Text(…, FontStyle, …). Naming GDI+ types in signatures is fine there; only creating GDI+ objects fails. So a browser front end can be written against the 1.x API, and the breaking step 8 (dropping System.Drawing.Common) is not needed for the browser.
• Pictures are only painted as their outline in such a renderer, because IPaintTo3D has only Bitmap members for images (0 bitmap calls in the run). Showing the image itself needs the optional image interface discussed for Make CADability.dll platform independent: remove GDI+ from the core, porting the ShapeIt work #412; that is a separate PR.

Notes

• No workload is needed. The plain WebAssembly SDK of .NET 10 builds it.
• The project is not added to CADability.sln, so building the solution in Visual Studio does not require the WebAssembly SDK.
• No change to CADability.dll or its public API.

Testing

Locally on Linux: dotnet build -c Release and node bin/Release/net10.0/wwwroot/main.mjs give "All checks passed." and exit code 0. The same program against master gives exit code 7.

🤖 Generated with Claude Code

https://claude.ai/code/session_01YXvDW91oXpy7RquGHNxgR5

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