fix(nx-plugin): allow project-root dist siblings in build outputs policy

The build.outputs policy required exactly ["{projectRoot}/dist"],
which clobbers repos that legitimately aggregate secondary dist
trees into the build target (AxE edb6a3d10: dist-node carries the
bun/node export condition, and omitting it from outputs served stale
builds). Validation now requires the canonical dist tree and admits only
{projectRoot}/dist-<suffix> siblings; the fixer resets outputs solely
when invalid, preserving valid extras instead of rewriting the array.