feat: Add bd init --contributor and --team wizards

- Implement OSS contributor workflow wizard
  - Auto-detects fork relationships (upstream remote)
  - Checks push access (SSH vs HTTPS)
  - Creates separate planning repository
  - Configures auto-routing to keep planning out of PRs

- Implement team workflow wizard
  - Detects protected main branches
  - Creates sync branch if needed
  - Configures auto-commit/auto-push
  - Supports both direct and PR-based workflows

- Add comprehensive documentation
  - examples/contributor-workflow/README.md
  - examples/team-workflow/README.md
  - Updated AGENTS.md, README.md, QUICKSTART.md
  - Updated docs/MULTI_REPO_MIGRATION.md

Closes: bd-kla1, bd-twlr, bd-6z7l
Amp-Thread-ID: https://ampcode.com/threads/T-b4d124a2-447e-47d1-8124-d7c5dab9a97b
Co-authored-by: Amp <amp@ampcode.com>

AGENTS.md

@@ -1048,6 +1048,16 @@ Happy coding! 🔗
 bd init --prefix bd
 ```
 
+**OSS Contributor?** Use the contributor wizard for fork workflows:
+```bash
+bd init --contributor  # Interactive setup for separate planning repo
+```
+
+**Team Member?** Use the team wizard for branch workflows:
+```bash
+bd init --team  # Interactive setup for team collaboration
+```
+
 **Check for ready work:**
 ```bash
 bd ready --json