Absorbs battle-tested knowledge from the v2 skill into the upstream
add-signal: registration paths (new number + linked device), CAPTCHA
flow, VoIP SMS-first timing, Java prereq, config-lock warning, wiring
SQL for groups, not_member silent-drop fix, GroupV2 groupId extraction
note, and UUID-based platform ID format.
Corrects a factual error in the upstream: DM platform IDs are
signal:{UUID} (ACI), not phone numbers.
Removes the now-redundant add-signal-v2 skill.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>