Support for Vulkan and ROCm/HIP GPU backends

[mwolson]

whisper-rs 0.16 exposes vulkan and hipblas feature flags (from whisper.cpp), but minutes doesn't wire them through yet. Adding these would let AMD GPU users (and anyone with Vulkan support) get hardware-accelerated transcription.

The change would be small, following the same pattern as the existing cuda/metal/coreml flags:

# crates/core/Cargo.toml
vulkan = ["whisper-rs/vulkan"]
hipblas = ["whisper-rs/hipblas"]

# crates/cli/Cargo.toml
vulkan = ["minutes-core/vulkan"]
hipblas = ["minutes-core/hipblas"]

Then users could install with:

cargo install minutes-cli --features vulkan
# or
cargo install minutes-cli --features hipblas

I haven't tested either backend myself, so I'm not sure if there are runtime quirks beyond wiring the features through. Happy to put up a PR if this seems reasonable.

[silverstein]

Yes, this is a clean addition. Wired the same way as cuda/metal/coreml, and we're already on whisper-rs 0.16, so it really is just the few feature lines you sketched out.

I'd love a PR. Two small things I'd ask for:

1. A short note in the README install section listing all four GPU backends and their build prereqs, so someone running cargo install minutes-cli --features vulkan knows they need the Vulkan SDK installed first (and same for ROCm with hipblas). That'll save us a stream of "build broke" issues later.

2. Mark vulkan and hipblas as experimental in that note, since neither of us has actually run them end to end. CUDA is in the same boat honestly, we don't exercise any of the GPU backends in CI, but Metal is the only one I personally dogfood every day. I'd rather be upfront about that than have someone install hipblas, hit a whisper.cpp quirk, and feel misled.

No need to touch CI or the Homebrew formula. Source-install only is the right scope.

If you hit anything weird while testing on your own hardware, please drop notes on the PR. AMD GPU support is something I've wanted for the Linux story but don't have the hardware to validate myself.

Thanks for offering to do the work!

[silverstein]

Thanks again for raising this and for following through with the PR.

This is now merged in #99, so Minutes supports the vulkan and hipblas feature flags for source installs, with the README/docs updated to call out prerequisites and mark both backends as experimental.

Really appreciate the contribution and the hardware validation notes on AMD/Vulkan too.