internal/rosa: expose supported architectures

This information is useful to external tooling and makes a lot more sense in this package than cmd/mbf. This change also fixes non-native artifact resolution during clean.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/rosa.go

@@ -443,12 +443,11 @@ func (t Toolchain) appendHandle(a []pkg.Artifact, pv pa, p ArtifactH) []pkg.Arti
 	}
 	pv[p] = struct{}{}
 
-	meta, _ := t.MustLoad(p)
+	meta, u := t.MustLoad(p)
 	for _, d := range meta.Dependencies {
 		a = t.appendHandle(a, pv, d)
 	}
-	_, d := t.MustLoad(p)
-	return append(a, d)
+	return append(a, u)
 }
 
 // Append recursively appends multiple [Artifact] named by their handles, and