feat(compositor): fall back to a WARP device when D3D11 hardware init fails

[EtienneLescot]

Scoping PR — no implementation yet. The branch carries a single empty commit so the PR can exist; drop it when the real work starts.

The problem

Both D3D11 devices are created hardware-only, with no fallback:

• poc-d3d/src/d3d.rs:43 — D3D11CreateDevice(..., D3D_DRIVER_TYPE_HARDWARE, ...), then bail! if the returned feature level is not 11_1.
• electron/native/wgc-capture/src/wgc_session.cpp:79 — same driver type.

So on a VM, over RDP, on a machine whose GPU does not reach feature level 11_1, or after a driver fault, the compositor does not start. It fails; it does not degrade.

This matters more than it used to: refactor(preview): remove the CPU and web fallbacks — one native path deliberately removed the preview's software route. There is now nothing behind the native path.

Scope

• Retry device creation with D3D_DRIVER_TYPE_WARP when the hardware attempt fails.
• Decide, explicitly, which surfaces accept a WARP device — preview, export, or both. WARP is a CPU rasteriser, so the frame rate will drop hard; shipping it silently for export may be worse than failing.
• Surface the degraded mode to the user rather than letting it read as "the app is slow today".

Open questions to settle in review

• Is WARP acceptable for export, or preview only?
• Does the WGC capture session need the same treatment, or is hardware capture a hard requirement anyway?
• What does the shader path cost under WARP — is it usable at all, or is a clear error the better product?

Depends on

Nothing blocking, but it shares a reflex with the encoder-selection PR: detect what the host actually offers, then degrade deliberately. Landing that one first would set the pattern.

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