Add read-only embedding inspection and population planning

[gkennos]

Pre-flight

• I searched existing issues and this has not been requested before.

Problem or motivation

Add supported APIs for inspecting an embedding store and planning vocabulary population without changing the store.

This allows setup tools to show what is configured, which embeddings already exist, and what needs to be populated or refreshed.

Proposed solution

• Inspect whether an embedding store is initialise & registered embedding models
• Read stored concept IDs
• Inspect existing PostgreSQL indexes
• Generate reviewed index-removal statements
• Explicitly initialize an embedding store as a separate writable operation
• Plan population by vocabulary and domain
• Stream large CDM and embedding-store reads in bounded batches.
• Reprocess concepts when their stored metadata no longer matches the CDM.

Alternatives considered

No response