Fix N+1 Query Issue in Vets Endpoint - created-by-agentic

[shaykeren]

This PR addresses the N+1 query performance issue in the /vets.html endpoint by:

1. Changing the Vet entity's specialties relationship from EAGER to LAZY fetching to prevent automatic loading of specialties
2. Adding @entitygraph and JOIN FETCH to VetRepository methods to optimize specialty loading with a single query
3. Adding an index on vet_specialties(vet_id) to improve join performance

Changes made:

• Modified Vet.java to use FetchType.LAZY for specialties
• Updated VetRepository.java to use @entitygraph and added optimized query method
• Added database index on vet_specialties.vet_id

These changes will eliminate the N+1 query problem by:

• Preventing automatic eager loading of specialties
• Using a single optimized query with JOIN FETCH when needed
• Improving join performance with the new index

Testing:

• Verified that specialties are loaded correctly with a single query
• Confirmed that the index improves join performance
• Ensured backward compatibility with existing code