Changes in version 0.1.0                        

Initial release

  - cat_spec(): Build a Causal Assignment Tree specification from panel
    data
  - cat_label(): Attach cohort letters and canonical labels to a spec
  - cat_plot_tree(): Unified plot dispatcher — automatically selects
    DiD, CSDiD, or DDD tree
  - cat_plot_did(): Publication-quality 2×2 DiD tree
  - cat_plot_csdid(): Publication-quality CSDiD tree (Callaway–Sant'Anna
    staggered adoption)
  - cat_plot_ddd(): Publication-quality DDD/DR-DDD tree with subgroup
    split
  - cat_counts(): Count units or observations per CAT node
  - cat_balance_table() / cat_balance_plot(): Covariate balance across
    nodes
  - cat_diag(): Pretrend diagnostic plots (DR-DDD and CSDiD)
  - cat_att_equation(): Returns the ATT formula implied by the tree
  - cat_save_png(): Save a CAT plot to a high-resolution PNG
  - Grayscale option (grayscale = TRUE) for black-and-white publications