Virtual controller QA isolation - 2026-10-21

smoke_sdl_gamepad previously selected the first available controller. With an
Xbox Series X Controller connected, the Nintendo virtual-device test read the
Xbox instead and failed its exact button assertion. This was a test isolation
failure; no production controller behavior was changed to make it pass.

The noninteractive test disables physical HIDAPI, RawInput, WGI, XInput,
DirectInput and GameInput backends using process-local SDL hint overrides,
before SDL initialization. It asserts zero devices before attaching its
virtual Nintendo controller and exactly that device afterward. Existing button,
axis, trigger, label and disconnect assertions remain. --watch returns before
isolation and continues to observe real controllers normally.

The revised target compiles and passes10consecutive runs; the full62-test
native suite passes afterward. This validates the virtual-device fixture and
does not establish new physical Bluetooth/controller hardware acceptance.
