v0.4.13 — panel-aware descriptives, histogram overlays, df_def-driven readability

0.4.13 (2026-06-24)

Explore

• explore_descriptive_table is now panel-aware. When a time column is known (declared
  via set_panel / set_labels, or passed explicitly) each statistic is shown by period
  — by default at the first and last period — under a spanning column header (e.g. Mean over
  2015 and 2025); without a time dimension it falls back to one column per statistic. The
  default statistics are now Mean, Std. dev., Median, Min., Max., rows are labelled from
  the data dictionary, and the notes report the number of observations and any variable with
  missing data. Breaking: the old length-8 digits vector is replaced by a stats=
  selection (any of the eight statistics), a scalar-or-mapping digits=, and a new periods=
  argument; the result gains a tidy .by_period frame (.df still carries all eight
  pooled statistics).
• explore_histogram gains opt-in density overlays. New kde= and normal= flags draw a
  Gaussian kernel-density estimate and/or a normal curve on the Density scale (off by default;
  the Count/Density toggle hides them in Count view).
• The trend / time-series plots no longer show a draggable range slider
  (explore_trend_plot, explore_quantile_trend_plot, explore_spaghetti_plot).

Data dictionary (df_def) everywhere

• Every function now leans on the data dictionary for readable output, while still working
  without it. Regression / estimation / CRE tables relabel their coefficient and
  dependent-variable rows from the dictionary (the tidy .df keeps raw term names), and the
  panel estimators (analyze_panel_table, analyze_hausman_test, analyze_cre_table) and DiD
  views (analyze_event_study, analyze_panel_view) now resolve entity / time / unit
  from the declared panel, so those arguments can be omitted after set_panel / set_labels.
• Examples across the library now illustrate the dictionary, opening with
  df = ex.set_labels(load_kuznets(), load_kuznets_data_def(), set_panel=True).