fix: convert tabularx to plain tabular in cards (eliminates table overflow)
tabularx resists all runtime patching (def, renewcommand, AtBeginDocument all fail). Solution: cards-convert.mjs now converts tabularx → tabular with p{0.28\linewidth} columns at generation time. The existing adjustbox wrapper on plain tabular handles any remaining overflow by scaling.
Results: sustainability 480pt overflow → 14pt, folk-songs 105pt → 0, whistlegraph 170pt → 0. All table overflows eliminated across the platter. Remaining overflows are paragraph text (long URLs/words).
Also changed source files to use XXX flexible columns (harmless on regular two-column PDFs, helps if anyone builds cards manually).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>