add WASAPI standalone backend

[erikgrahn13]

Summary

• add a Windows WASAPI shared-mode backend and make it the standalone default
• use IAudioClient3 low-period streams when available with an IAudioClient fallback
• support stereo capture and rendering, default-device enumeration, COM/MMCSS lifecycle, and output-parameter publication
• compensate independent capture/render clock drift with a bounded adaptive stereo resampler
• continue compiling and linking the existing ASIO backend for future runtime backend selection

Why

Windows standalone applications should start reliably with the system audio stack without requiring an installed ASIO driver, while retaining ASIO for a future user-selectable pro-audio path.

Validation

• git diff --cached --check
• cmake --build build --parallel (Linux Release example applications)
• Windows compilation and device-level WASAPI testing are pending GitHub Actions and Windows hardware validation

[chatgpt-codex-connector]

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