Fix linter issues and test failures

- Fix spelling: cancelled → canceled, cancelling → canceling
- Remove unused error return from performFlush() function
- Check cmd.Help() error return in search.go
- Fix file permissions in gitignore.go (0644 → 0600)
- Update tests to match performFlush signature change
- Remove unused os import from flush_manager.go

cmd/bd/doctor/gitignore.go

@@ -94,8 +94,8 @@ func CheckGitignore() DoctorCheck {
 func FixGitignore() error {
 	gitignorePath := filepath.Join(".beads", ".gitignore")
 
-	// Write canonical template with standard git file permissions (world-readable)
-	if err := os.WriteFile(gitignorePath, []byte(GitignoreTemplate), 0644); err != nil {
+	// Write canonical template with secure file permissions
+	if err := os.WriteFile(gitignorePath, []byte(GitignoreTemplate), 0600); err != nil {
 		return err
 	}