Four checks, run before anything is linked into Dirt-Samples.

grade is deliberately re-run over the WRITTEN FILES rather than trusted from the
finder's in-memory scoring: same verdict by a different code path, so a disagreement
means one of them is wrong, which is the entire reason to run it twice.

Bank shadowing is the one that would hurt silently. loadSoundFiles defaults to
appendToExisting = false, so a new folder whose basename matches an existing bank frees
that bank's buffers and takes the name — no error anywhere, and the only symptom is that
an old track now plays the wrong sound. Checked BEFORE linking, through tools/pvbanks.py
so this and bank-check.py cannot disagree about what a bank is.

Rights is advisory and never blocks the load, because loading a kit locally is not
releasing a track — but it does say out loud when a kit cut from someone else's stems
is not yet ledgered.

Self-test on the synthetic pack immediately blocked on clipping in the fixture, which
is the fixture's fault and the gate's point.