#5 label/milestone/task render writes bare scalars that re-parse as int/float/bool

label create --name 123 --color true writes unquoted; reload fails: invalid type integer/float. Same esc()/plain() in label.rs milestone.rs task.rs. Live .forge/labels.md has color 5319E7 bare -> label list broken. Fix: quote YAML-risky scalars on write.