feat: integrate detect-pollution into bd doctor --check=pollution (bd-kff0)

- Add --check flag to doctor for specific check modes
- Add --check=pollution to run detailed pollution detection
- Add --clean flag to delete detected test issues
- Mark detect-pollution command as hidden (deprecated)
- Update fix messages to point to new doctor --check=pollution

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

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

cmd/bd/doctor/validation.go

@@ -304,7 +304,7 @@ func CheckTestPollution(path string) DoctorCheck {
 		Status:  "warning",
 		Message: fmt.Sprintf("%d potential test issue(s) detected", count),
 		Detail:  "Test issues may have leaked into production database",
-		Fix:     "Run 'bd detect-pollution' to review and clean test issues",
+		Fix:     "Run 'bd doctor --check=pollution' to review and clean test issues",
 	}
 }