* fix(examples): harden multi-agent notepad 409 retry and improve docs
Add decorrelated jitter to the GitHub Contents API retry loop so racing
workers don't retry in lockstep, and widen the retry set to 5xx for
transient server errors. Without jitter, N concurrent workers trip the
same backoff schedule and re-collide on each beat.
Also:
- Extract the inline 220-line sandbox runner from demo.sh into a
separate runner.sh. demo.sh stays as host orchestration; runner.sh
is the per-sandbox program. demo.sh shrinks 460 to 240 lines.
- Rewrite README to lead with "Why GitHub as a shared notepad?" and
add a "Memory architecture variants" section covering pile,
append-journal, and indexed-memory patterns.
- Switch Quick Start to use \`gh auth token\` as the primary path.
- Pass the worker slice arg explicitly instead of reading \$9 from the
outer dispatcher.
- Add .gitignore for personal run_demo.sh helpers.
* docs updates
Drew Newberry