List targets and run any target by label

Run fabrik targets to list every declared target across the workspace, or fabrik run //package:name to load the workspace, find the matching target, and run the action that produces it through the cache. For a rust_binary, that action compiles with rustc and writes the resulting binary to .fabrik/out/<package>/<name>. The old fabrik build verb was removed and folded into the uniform run verb, so the same CLI surface applies to all target kinds.