Adds breadmill's `full` feature (npu + rocm + cuda together) and switches
the release workflow to build with it. All three backends are ort's
load-dynamic (dlopen) mode, so combining them doesn't require the NPU/ROCm/
CUDA toolkits on the build host -- which backend is actually available is
resolved at runtime via ORT_DYLIB_PATH / the dynamic linker, per whichever
backend is selected for that run.
Also fixes a real bug this surfaced: backend selection checked
`config.model.backend == "rocm"` unconditionally in an if/else-if chain, so
an explicit --cuda (or --npu) flag silently lost to an unrelated `backend`
value already sitting in config.toml. CLI flags now always take priority
over config.
Version bump: breadmill 0.2.0 -> 0.2.1.
GitHub Actions self-hosted runners need per-repo registration on a
personal account; Forgejo Actions' runner already serves every repo
with zero setup. Moves release publishing there (dl.breadway.dev stays
the primary bakery target; GitHub release upload is kept as the
fallback via an explicit token, since Forgejo Actions has no ambient
GITHUB_TOKEN) and adds a mirror workflow to keep GitHub in sync
automatically.
