MX Master 4: button remapping card

[weltern]

Surfaces feature 0x1B04 (added in OpenMouse-Project/mouse-protocol#11,
which this depends on) as a card in the Buttons tab. Needs that package version
to build.

Follow-up to #82 (merged), which brought the haptics/wheel/name/Easy-Switch
cards. Verified on hardware: MX Master 4 over a Logi Bolt receiver 046d:c548.

The limitation, up front

This remaps control → control only — a button acts as another button the
device already knows. It does not do Options+-style actions ("launch an
app", "switch desktop"); those work by diverting the button and handling it in
vendor software, which the web app has nothing to receive. So the card offers
remapping and a way to hand diverted buttons back, never a way to divert them.

What the card shows

Every reprogrammable control the mouse reports gets a dropdown whose options are
the targets the device's own group mask allows. Two deliberate choices:

• Left and right click are shown but locked, with a note that the firmware
  is what prevents remapping them (their group mask is zero). Showing them fixed
  reads as a restriction rather than a missing button.
• Virtual controls are hidden. The MX Master 4's "virtual gesture button" is
  the event its gesture button emits when held and dragged — not something a
  user can press — so a row for it is noise.

Staging

A remap stages like any other write and shares one group, so several apply
together. The controls are not part of MouseStatus, so there is no preview;
the card renders the staged mapping from the snapshot (the same way staged
profile names and rates already are), which is what holds the dropdown on the
picked target until it is flashed and returns it on revert.

Restoring diverted buttons is immediate, not staged

Deliberately. A diversion is state another application left in the mouse, not a
preference this user expressed, and the button does nothing at all until it is
cleared — staging that repair behind a flash step would leave a dead button dead
for no reason. Options+ uses the temporary divert flag, which the mouse clears
itself when Options+ stops, so this is mostly a manual escape hatch.

Reads

The control table is two round-trips per control, too much for the five-second
refresh, so it is read once on connect and re-read after a write — the same
reason the Easy-Switch and friendly-name reads are cached.

Testing

• npm run check green (51 tests), including availability tests that the
  card appears only when the mouse reports controls and never for a non-Logitech
  device.
• On hardware (MX Master 4 over Bolt): remapped the gesture button to middle
  click, flashed, confirmed by pressing it, reloaded to confirm it persisted,
  reverted, and confirmed the dropdown holds the staged pick before flashing and
  returns to the device value on revert. Diverted/restore exercised against Logi
  Options+.

[weltern]

The failing check job is the cross-repo dependency, not a problem with this PR's code.

@openmouse/protocol is pulled from mouse-protocol's default branch, so the button codec it relies on (logitechControlName, LogitechReprogrammableControl, and the driver's readButtons / setButtonMapping / clearButtonDiversion) isn't present until the companion PR merges. Every error in the log traces back to that — including the lone target: any, which only appears because remappableTo loses its number[] type when the import fails.

Merge order: OpenMouse-Project/mouse-protocol#11 first, then a re-run of this PR's check builds green. Same dependency shape as #82 → #9.