feat(agents): add LLM provider layer with failover and PII-tier gating

feat(scoring): implement the deterministic Phase 4 scoring core

feat(search): add Phase 2 semantic search with pgvector and hybrid retrieval

feat: scaffold CV screener serving layer with ingestion pipeline, REST API routers, repositories, storage, parsing, security, and integration/unit test foundations

feat(api): add Phase 0-1 backend for identity and document ingestion