v0.1.5 — fix ColumnsModal crash on duplicate column names

Fixed

• TUI Columns modal crash on slugs with duplicate column names.
  Eleven slugs ship parquet schemas with legitimately repeated
  top-level column names — the osmi-mental-health-in-tech-* survey
  series (2016 through 2023) repeats "Why or why not?" follow-ups
  under each yes/no item, and uci-spambase, uci-parkinsons, and
  uk-price-paid each have one or more repeated headers. The new
  Columns modal used the bare column name as the Textual DataTable
  row key, so the second occurrence crashed with DuplicateKey.
  Repeated names are now suffixed with (2), (3), etc. for
  display + lookup; the by-name stats dict no longer silently
  collapses entries either. The underlying parquet's column names
  are unchanged.