Fix N+1 Query Issue in Owners-Pets Retrieval-created-by-agentic

[asafchen-dig]

There is an N+1 query performance issue in the /owners endpoint where the application makes one query to fetch owners followed by N separate queries to fetch each owner's pets.

Root Cause:

• EAGER fetching of pets collection in Owner entity
• Missing fetch join optimization in repository queries
• No batch fetching configuration

Solution:

1. Changed fetch type to LAZY to prevent unnecessary loading
2. Added @EntityGraph for optimized loading when needed
3. Implemented @batchsize for efficient batch fetching

A pull request has been created with these changes: #433

This issue is being tracked as part of incident #6b373e96-616c-11f0-a2c1-c67c199f5e31