Schedule: Add unit tests to utils/get-random-item.ts

[gitauto-ai]

Resolves #608

Summary

Add comprehensive unit tests for utils/get-random-item.ts to cover happy paths, edge cases, and error scenarios with deterministic assertions.

Test Patterns

• Selects a valid element from a non-empty array.
• Deterministic selection by mocking Math.random (e.g., 0, mid-range, and near-1) to hit boundary indices (0 and length - 1).
• Single-element array always returns that element.
• Handles arrays with falsy values (0, '', false, null, undefined) without filtering them out.
• Does not mutate the input array.
• Defined behavior on empty arrays (returns undefined or throws a specific error).
• Works with arrays of objects and mixed types (returns the actual reference).
• Handles sparse arrays (holes) appropriately.
• Basic large-array smoke test to ensure consistent behavior.
• Restores Math.random after each test to prevent cross-test leakage.

git fetch origin
git checkout gitauto/issue-608-20260119-000049-2rtk
git pull origin gitauto/issue-608-20260119-000049-2rtk