Add chunk_max_bytes and chunk_count columns to embedding_metadata to
support config drift detection and adaptive dedup sizing. Includes a
partial index on sentinel rows (chunk_index=0) to accelerate the drift
detection and max-chunk queries.
Also exports LATEST_SCHEMA_VERSION as a public constant derived from
the MIGRATIONS array length, replacing the previously hardcoded magic
number in the health check.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
