Follow-up review: firmware learning reference (bmad-loop story 10-4) #127

Tracks Zoho task EPM-T143 (Coldframe V1 – bmad-loop story 10-4: Firmware Learning Reference).

Follow-up review pass on the firmware learning reference merged in #126, which recommended a second check of the cited constants and symbols in docs/firmware/ against the source. Scope: fix whatever the review confirms, in docs and comment-only proto changes.