Introduce production vector-store abstraction

[ishaanxgupta]

We are tightly coupled to Pinecone through pinecone.py, with limited filter support and no schema migration/recovery layer.

Acceptance criteria:

• Define VectorStore interface.
• Support Pinecone plus one production alternative.
• Add filter DSL, batch query/upsert/delete, namespace migration, and metadata validation.
• Add integration tests with fake and real adapters.

[ishaanxgupta]

Update: VectorStore interface and pinecone support has been added.