v0.6.2 — pin-and-enforce speed mode, with Auto release

Changed

• CC2 speed-mode persistence redesigned as pin-and-enforce. The
  0.6.1 snapshot-per-switch restore lost an arms race with the
  firmware: after eight consecutive successful restores, a reset
  arriving outside the covered window (late after a restore, or
  mid-print with no switch at all — observed 2026-07-05 ~15:00)
  poisoned the baseline and silently disabled every restore after it.
  The firmware only ever resets TO balanced, so the model is now: the
  mode you set is pinned (immediately via pycentauri; after holding
  15 s when set from the touchscreen, since a non-balanced mode can
  only come from a human), and any disagreement lasting 12 s while
  printing is re-applied, at most every 30 s. One consequence,
  deliberate: while a mode is pinned, selecting balanced from the
  touchscreen is indistinguishable from a firmware reset and will be
  reverted — switch to balanced through pycentauri instead, which
  re-pins. Pins clear when the print ends, and speed auto (CLI),
  {"mode": "auto"} (HTTP), or the web UI's Auto button release the
  pin explicitly, returning speed control to the printer.
• Root cause fully mapped (wire captures, 2026-07-05): every reset is
  a service operation — full filament switches, plus brief nozzle
  wipe / purge operations at the chute that are too short to register
  as "switching" — and a human's touchscreen tap is byte-identical to
  a firmware reset on the wire, so balanced-from-touchscreen cannot be
  auto-detected while a pin is active. Use Auto or set balanced via
  pycentauri instead.