Two faults that hid each other, both found by reading the journal — which is
exactly the work this doctor exists to save.

It probed sys.executable. PLN's PATH starts with a pyenv shim, so the natural
`python3 tools/rig-doctor.py` answered for pyenv 3.11.10 — an interpreter no unit
ever uses; all five python units run /usr/bin/python3. That made the doctor wrong
in both directions at once: it called mido and PyQt5 MISSING while every unit
using them ran fine, and it still could not see the dep that was genuinely gone.
A check that cries wolf is a check nobody reads the day it is right. So it now
asks the interpreter the rig actually runs on.

And the dep it could not see: midiviz imports PySide6, and has since it was born
(30a704ec), but the table listed "perf-tray, midiviz GUIs" against PyQt5 alone.
So the doctor asked about a binding midiviz does not import, found it, and
reported green while midiviz crash-looped at RestartSec=5 on ModuleNotFoundError
for a whole session, PLN's lens simply absent. Two GUIs, two bindings, two rows.

Run the natural way it now says: CAN THIS BOX PLAY A SET? no — python: PySide6.