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>
