Sequential DB queries to minimize CPU load + optimized caching for leaderboards

[sfreeman422]

• Fix linting errors: remove if (!userData) / if (!leaderboards) null guards that ESLint flagged as @typescript-eslint/no-unnecessary-condition — TypeScript's control flow analysis already narrows both to non-null after the try-catch (catch always rethrows, so reaching the spread means the try succeeded)

[Copilot]

Pull request overview

This PR refactors the backend dashboard data fetch path to reduce concurrent DB query load and to improve cache reuse by splitting dashboard caching into per-user and per-team (leaderboards) entries.

Changes:

• Split Redis caching into dashboard:user:{teamId}:{userId}:{period} and dashboard:leaderboards:{teamId}:{period} and merge on read.
• Replace parallel Promise.all dashboard queries with sequential queries to reduce concurrent DB pressure (including sequential leaderboard queries).
• Extend Jest tests to validate new cache keys and merged split-cache behavior.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
packages/backend/src/dashboard/dashboard.persistence.service.ts	Splits cache keys/values and makes dashboard + leaderboard DB queries sequential.
packages/backend/src/dashboard/dashboard.persistence.service.spec.ts	Updates cache key assertions and adds coverage for merged split-cache reads without DB queries.

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[sfreeman422]

@copilot fix linting errors

[Copilot]

@copilot fix linting errors

Fixed in commit 2939b49. The null guards I added were flagged by @typescript-eslint/no-unnecessary-condition as "value is always falsy" — TypeScript's control flow analysis already narrows both userData and leaderboards to non-null after the try-catch block (since the catch always rethrows, reaching the spread guarantees the try succeeded and both were assigned). Removed the guards; the spread is already type-safe.