Extract PRAutoBlogger_Generation_Lock (DB mutex) and
PRAutoBlogger_Ajax_Handlers (image/model/test AJAX) from the
482-line executor. Executor retains generation cron/AJAX + model
registry at 299 lines. Document background generation flow in
ARCHITECTURE.md.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
