fix(sidebar): always sort the "Other" section to the bottom

[rafaeelaudibert]

Summary

In the sidebar, the Other section (tasks without a resolvable repository) was being sorted alphabetically alongside the repository sections. It should always sit at the bottom.

This pins the "other" group to the bottom in both sort paths of groupByRepository:

• the alphabetical fallback (no persisted folder order)
• the persisted folder-order path

via a small pinOtherLast comparator helper.

Testing

• Added two tests covering "Other" sorting last in both paths.
• pnpm --filter @posthog/core test groupTasks → 20 passed.

🤖 Generated with Claude Code

[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit 5bbab33.}