fix: CNN test tool GPU readback with wgpuDevicePoll

Fixed buffer mapping callback mode mismatch causing Unknown status.
Changed from WaitAnyOnly+ProcessEvents to AllowProcessEvents+DevicePoll.

Readback now functional but CNN output incorrect (all white).
Issue isolated to tool-specific binding/uniform setup - CNNEffect
in demo works correctly.

Technical details:
- WGPUCallbackMode_WaitAnyOnly requires wgpuInstanceWaitAny
- Using wgpuInstanceProcessEvents with WaitAnyOnly never fires callback
- Fixed by using AllowProcessEvents mode + wgpuDevicePoll
- Removed debug output and platform warnings

Status: 36/36 tests pass, readback works, CNN shader issue remains.

handoff(Claude): CNN test tool readback fixed, output debugging needed

0 files changed, 0 insertions, 0 deletions