Title: Add integration test for leaderboard cache warming

[Emmyt24]

Description
Implement integration test verifying leaderboard cache is correctly populated on first query.

Requirements and context

• Must be secure, tested, and documented where applicable
• Should stay reviewable and fit the current monorepo structure

Suggested execution

• Create branch: add-integration-test-for-leaderboard-cache-warming
• Keep changes scoped to the issue and reference the task IDs in the PR

Implement changes

• Clear cache before test
• Execute first query and measure time
• Execute second query and verify it's faster (cached)
• Assert cache contains correct data

Test and commit

• Run the most relevant tests for the touched service or UI surface
• Include cache warming metrics
• Call out edge cases, assumptions, and any follow-up work

Example commit message

test: add leaderboard cache warming integration

Guidelines

• Prefer small, reviewable PRs
• Keep naming and data contracts consistent with the spec docs
• Preserve responsive and accessible behavior for frontend work

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