Add read-only structure tools: search_structures (per character), get_structure and get_structure_market (single structure via one token), and get_corp container logs. New charutil.one_token helper picks a single authenticated token (named character or first). 31 tools total, 75 tests, coverage 92%. Closes #21. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>