chore(driver): retire roles/driver/ in favor of scripts/driver/ (#3)

The driver is a script under scripts/, not a role under roles/.
roles/ holds agent context fragments only (per the scripts/ layout
pivot landed in 564372a). A subagent invoked by the driver still
reads its own roles/<role>/AGENT.md, but no AGENT.md exists for the
driver itself; scripts/driver/README.md is the human-facing
overview.

Removes roles/driver/AGENT.md. The driver.sh that lived alongside
moved to scripts/driver/driver.sh in 564372a, so roles/driver/ is
now empty and removed by git.

Per designs/driver.md § Retired / superseded.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: endolinbot