Add two new doctor checks:
1. persistent-role-branches: Detects crew/*, witness/rig, refinery/rig
directories not on main branch. Persistent roles should work directly
on main to avoid orphaned work.
2. beads-sync-orphans: Detects code changes on beads-sync branch that
weren't merged to main, catching cases where merges lose code changes.
Also adds ensureMainBranch() to crew attach to auto-switch persistent
roles to main at session start.
Closes gt-p9zh
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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