Ship one binary with NPU + ROCm + CUDA support, fix CLI flag precedence

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.

Cargo.lock

@@ -133,7 +133,7 @@ dependencies = [
 
 [[package]]
 name = "breadmill"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
  "breadsearch-shared",
  "hex",