Resolve a name or CUI to candidate companies.

A query that normalizes to a CUI resolves to that company alone, mirroring the site's AC1 rule: pasting a CUI must return the company it identifies, not whatever the name index happens to rank above it. A quoted query (q="mina srl") takes /cauta's exact-name path — the branch is inside search_companies, so REST, MCP and the site read quotes identically.