v0.4.15 — Explore case-study redesign

Explore

• The Explore page is now a single-pass Kuznets case study. A complete redesign walks newcomers through all 21 explore_* functions (and the set_panel / resolve_panel / treat_outliers utilities) once each, in the order an analyst actually works: know the panel's skeleton (explore_panel_structure, explore_missing_values_plot, explore_value_heatmap) → describe variables → split within vs between variation (explore_xtsum_table, explore_spaghetti_plot) → trends (incl. explore_distribution_over_time) → compare groups → relationships and the N-shaped curve (incl. explore_scatter_plot_within_between) → dynamics (explore_transition_matrix, explore_within_persistence). The eight previously-undemonstrated panel-aware functions now appear in the narrative.
• The Explore Streamlit app mirrors the case study. Its pages are reorganized to the same workflow — Overview & Data, Describe variables, Within & between, Trends, By group, Relationships, Dynamics — replacing the single catch-all "Panel structure" page. The Colab notebook is regenerated from the redesigned page.