When bd worktree creates a worktree, it writes a .beads/redirect file
pointing back to the main repo's .beads/. If this file is accidentally
committed (e.g., via git add .), it causes "redirect target does not exist"
warnings when cloned or used in other worktrees.
Changes:
- Add 'redirect' to GitignoreTemplate to prevent future accidental commits
- Add 'redirect' to requiredPatterns so bd doctor detects outdated .gitignore
- Add CheckRedirectNotTracked() to detect already-tracked redirect files
- Add FixRedirectTracking() to untrack accidentally committed redirects
Tests: 8 new tests covering template, detection, and fix scenarios
c98f5827bf