feat: Add attention mode to Active Tasks sidebar

[BnayaZil]

Problem

The Active Tasks sidebar had two scope modes (project / global) but no way to quickly surface the tasks that actually need the user's input. Tasks in `user-questions` or `review-by-user` were mixed in with in-progress and AI-review work, requiring the user to scan the full list to find what's blocking them.

Solution

• Added a third scope `"attention"` to `SidebarScope` (`"project" | "global" | "attention"`)
• Replaced the project/global toggle switch with 3 plain icon buttons: folder (project), globe (global), bell (attention) — all three sit naturally side-by-side, no toggle needed
• In attention mode: fetches all-project tasks (reuses the global fetch), filters to `user-questions` + `review-by-user`, sorted oldest-first so the longest-waiting task is always at the top
• Bell shows a pulsing amber count badge when attention tasks exist and the mode is not active
• Project badge shown for tasks from other projects (same as global scope)
• Empty state: "Nothing needs your attention"
• Scope persisted to `localStorage` like before
• `"Did you know?"` tip added for the new bell feature
• i18n keys added for EN / RU / ES
• Updated test that was asserting on the now-removed toggle `data-testid`

Extra information

• `ATTENTION_STATUSES` mirrors the same constant already defined in `ActivityOverview.tsx`
• The global fetch (`getAllProjectTasks`) is reused — no new RPC needed