Add standalone embedding-store initialisation command & model registration command

[gkennos]

Pre-flight

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

Problem or motivation

Makes headless registration easier for groundworkers setup

Proposed solution

1. Add CLI command to create embedding registry metadata table and required backend schema without registering a model or ingesting embeddings.
2. Add another command to simply register a model without needing to create embeddings.

Both commands need to be safe to re-run.

Alternatives considered

No response