When running `bd init` from a directory with a .beads/redirect file
pointing to a canonical .beads/ that already has a database, init
now errors instead of silently overwriting the existing database.
This prevents accidental data loss when:
- A project uses redirect to share a canonical database
- Someone runs `bd init` from the redirected location
- The canonical database was already initialized
The error message clearly explains:
- What happened (redirect target already has database)
- Where the redirect points to
- How to use the existing database (just run bd commands normally)
- How to reinitialize if needed (rm the database first)
Adds test: TestInitWithRedirectToExistingDatabase
Part of GH#bd-0qel
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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