fix(sidebar): scope attention sorting to projects and workspaces

[im-ian]

Summary

Waiting and error tab priority now stays within the sidebar container where the tab belongs, preventing multi-tab source workspaces from jumping around as session status changes.

1. Container-scoped priority — prioritize direct sessions within their project and nested sessions within their own workspace, while preserving the existing project-level promotion for workspaces with zero or one tab.
2. Consistent drag behavior — use the same workspace tab-count rule for drag priority groups so displayed positions remain reachable and stable.
3. Clearer settings copy — describe the project/workspace boundary and single-tab exception in English, Korean, Japanese, and Simplified Chinese.
4. Regression coverage — cover multi-root source workspaces, the single-tab fallback, internal session ordering, and reliable settings-toggle synchronization.

Expected impact

Scenario	Before	After
Source workspace with multiple tabs	The entire workspace could jump to the project top when one tab needed attention	The workspace keeps its manual slot; only the waiting/error tab moves to the top inside it
Workspace with zero or one tab	The workspace moves into the project's priority group	Unchanged
Project-direct tabs	Waiting/error tabs move ahead of ready work in the project	Unchanged
Saved manual order	Preserved beneath the temporary priority view	Unchanged

Design notes

• folderGroupHasProjectPriorityStatus promotes a workspace row only when it has at most one session and that session needs attention.
• Multi-tab workspaces remain in their saved top-level position; orderSessionsByPriority continues to stable-partition their child sessions internally.
• The drag priority index uses the same predicate as display ordering, avoiding drops into slots that the next render would immediately undo.

Test plan

• pnpm run test — 109 files, 1,290 tests passed
• pnpm run typecheck — passed
• pnpm run build — production build passed
• pnpm exec playwright test tests/e2e/sidebar.spec.ts --grep "priority sorting" --workers=1 --repeat-each=3 — 6/6 passed
• git diff --check — passed