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- Add redirect to requiredPatterns for outdated gitignore detection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.go

@@ -412,9 +412,9 @@ func runDiagnostics(path string) doctorResult {
 	result.Checks = append(result.Checks, issuesTrackingCheck)
 	// Don't fail overall check for tracking issues, just warn
 
-	// Check 14b: Redirect file not tracked (worktree support)
-	redirectCheck := convertWithCategory(doctor.CheckRedirectNotTracked(), doctor.CategoryGit)
-	result.Checks = append(result.Checks, redirectCheck)
+	// Check 14b: redirect file tracking (worktree redirect files shouldn't be committed)
+	redirectTrackingCheck := convertWithCategory(doctor.CheckRedirectNotTracked(), doctor.CategoryGit)
+	result.Checks = append(result.Checks, redirectTrackingCheck)
 	// Don't fail overall check for redirect tracking, just warn
 
 	// Check 15: Git merge driver configuration