The night's lesson, converged: the driver only ran when a session remembered to
start it, then the session's background task got OOM-reaped and the surface sat
untranslated with every check green.

- tools/lcxl3-driver.service: repo-owned unit like its siblings; retry-forever
  hotplug posture; Conflicts=lcxl-leds-watch so exactly one painter owns the
  board; follow-mode (no --track) so paint tracks the loaded file.
- rig_units.py: lcxl3-driver + perf-tray rows (THE list is complete again),
  new 'manual' boot policy so --ensure can never start the v2 painter into a
  Conflicts= kill; --list --boot filter for shell consumers.
- parvagues-gear: moved into the repo; derives its sets from rig_units --list
  instead of being the fourth hardcoded copy; autostart-on now defers to
  --ensure (it used to enable parvagues-sc at login against policy).
- gig-up.sh leds(): detects the plugged surface generation and hands the LCXL3
  to the driver unit; v2 path invoked via python3 (exec-bit-proof).