Performance: N+1 query audit and batched data loading

[joelpeace48-cell]

Context

List endpoints (campaigns with referral counts, dashboards) likely issue per-row follow-up queries
(N+1), which collapse under load.

Scope

• Audit endpoints for N+1; batch with joins or dataloader-style batching.
• Add query-count assertions in tests for key endpoints.

Acceptance criteria

• Key list endpoints issue a constant number of queries regardless of row count.

Verification

• Tests assert query count stays flat as result-set size grows.

[gloskull]

Hello, I have 4 years of experience delivering solutions for projects like this, covering backend, frontend, and smart contract development. After carefully reviewing your requirements, I have a clear understanding of the task and am confident in my ability to deliver a clean, efficient, and thoroughly tested solution on time. I prioritize code quality, maintainability, and industry best practices throughout the development process. My PR will be submitted in under 10hours.