Add check to prevent 'bd init' from running inside a git worktree.
Worktrees should share the .beads database from the main repository,
not create their own.
The error message guides users to:
1. Run 'bd init' from the main repository
2. Use 'bd worktree create' to create worktrees with proper
redirects
This prevents the confusing behavior where init would create files
in unexpected locations or fail with "pathspec '.beads/.gitignore' did
not match any files" errors.
According to docs/WORKTREES.md, the proper workflow is:
- Initialize beads once in the main repository
- Use 'bd worktree create' to create worktrees with redirect files
- All worktrees share the single .beads/ database via redirects
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
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