ensure_embedding_dimension() now also checks and migrates mental_models.embedding,
fixing silent failures when changing embedding model dimensions. Extracted shared
per-table logic into _migrate_table_embedding_dimension() to avoid duplication.
Adds test coverage for the mental_models dimension migration path.
Fixes#523
Add ZeroEntropy as a reranker provider using their Rerank API
(https://docs.zeroentropy.dev/models). Supports zerank-2 (flagship)
and zerank-2-small models via direct HTTP API calls with httpx (no
additional SDK dependency required).
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
