fix: prevent .beads/redirect from being committed (GH#814)

- Add redirect to GitignoreTemplate with explanatory comment
- Add redirect to requiredPatterns for outdated gitignore detection
- Add CheckRedirectNotTracked() to detect already-tracked redirect files
- Add FixRedirectTracking() to untrack via git rm --cached
- Register check in bd doctor under Git Integration category
- Add 6 tests for the new functionality

The redirect file contains a relative path that only works in the
original worktree. When committed, it causes warnings in other clones:
"Warning: redirect target does not exist"

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

cmd/bd/doctor_fix.go

@@ -225,7 +225,7 @@ func applyFixList(path string, fixes []doctorCheck) {
 		switch check.Name {
 		case "Gitignore":
 			err = doctor.FixGitignore()
-		case "Redirect Not Tracked":
+		case "Redirect Tracking":
 			err = doctor.FixRedirectTracking()
 		case "Git Hooks":
 			err = fix.GitHooks(path)