Add three new bd doctor checks for redirect configuration health:
1. CheckRedirectTargetValid - Verifies redirect target exists and
contains a valid beads database
2. CheckRedirectTargetSyncWorktree - Verifies redirect target has
beads-sync worktree when using sync-branch mode
3. CheckNoVestigialSyncWorktrees - Detects unused .beads-sync
worktrees in redirected repos that waste space
These checks help diagnose redirect configuration issues in
multi-clone setups like Gas Town polecats and crew workspaces.
Closes bd-b88x3
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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