Add index.md to: star-systems, corporations, factions, technology,
contraband, concepts. Each lists its contents with brief descriptions.
Rewrite wiki/index.md to link to category indexes instead of inlining
all entries. Regenerate catalog-index.md from DB (remove redundant
System ID column after S-number migration).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
