transcripts: update SKILL.md for audio→transcripts / screen→percepts rename
Code renamed in March (f8bd2868, bf1cab94) but skill still taught the
deprecated --audio / --screen flags as primary. Update source-flag table,
source-type meanings, scan description, and example to match current code.
Keep --audio / --screen mentioned as hidden aliases. Also add "Invoke via
Bash" line and literal command names to TRIGGER.
Part of skills audit req_loq3e2lk pass 1+2.