docs(board): the LCXL3 answers three open questions and opens a new one

The board carried 'can third-party SysEx paint arbitrary text to the OLED?'
as UNVERIFIED, with a note that it mattered: HUD v2's alarms are derived
state, not control values, so a closed OLED meant the alarms stayed on
screen. The official programmer's reference settles it — arbitrary 128x64
bitmaps, and the firmware ACKs each frame specifically so you can animate.

Two more close the same way. LED brightness is CC 111 and non-volatile, so
open taste call #11 stops being an argument about whether a bypassed filter
should be bright and becomes a knob. And endless encoders emit deltas, so
pot-pickup does not exist to solve.

The new one is worse than the ones it closed. DAW mode is the only mode the
guide documents paint in, and DAW mode's CC map is fixed and PARTLY OVERLAPS
v2's with different meanings: v2's row-B knobs 29-36 are v3's row 3, and
v2's faders 77-84 are v3's relative-encoder row 1. Nothing errors. Controls
just move one row. That is the exact failure class b5ad8b6c spent 169 files
fixing, so that branch does not merge until this is settled.

Also retracted, with evidence: DIN is not our answer to the USB-hub single
point of failure. aconnect shows only Midi Through and the controller — this
machine has no MIDI DIN input at all, so DAW mode disabling the DIN outputs
costs nothing today.

And snare is still not cleared. 'Also a default tidalcycles CC0 pack' is a
name collision: upstream tracks 52 files under sn/ and zero under snare/.
The 90-file snare bank is local and unidentified, and still gates 4 tracks.

CosmicFest is closed as a mastering input by PLN's call. Five probes agree
nothing was captured to this machine; he had a stage mic and rates it poor.