Text rendering and window chrome

Windows build has broken text rendering and no title bar. Fix the rendering pipeline and add proper window chrome so the app looks and feels native on Windows.

Audio capture

Windows has no system audio capture — the macOS-specific implementation doesn't carry over. Implement system audio capture using wasapi-rs so transcription works on Windows.

GPU-accelerated transcription

Whisper.cpp runs CPU-only on Windows because there's no Vulkan build. Add Vulkan build support via scripts/pre_build.py for GPU-accelerated transcription. Can be deferred per @ComputelessComputer.

Windows CI gate

No CI ensures Windows builds stay working. Establish a Windows CI gate so regressions get caught before they ship.

Merged from

• Windows build stabilize #1469 — Windows build stabilize