Introduce built-in eval system for testing LLM response quality against
golden sets. Includes eval runner with 4 match strategies (exact,
contains, regex, custom), a pre-loaded 10-case golden set, REST API
endpoints for managing and running suites, and a dashboard UI under
Analytics → Evals with real-time progress tracking and pass rate
summaries. Also adds OpenAPI tags for Audio, Moderations, and Rerank.