Add sidebar row context menus

[SawyerHood]

Summary

• Use the shared Radix/shadcn-style context-menu primitive so sidebar thread and project rows open their actions menus at the right-click pointer location.
• Keep the existing ellipsis dropdown menus intact while sharing the same menu item content/action handlers with the context menus.
• Preserve left-click navigation/selection behavior for thread and project rows.
• Dismiss right-click-opened menus on action selection, outside click, and Escape.
• Add focused coverage for default thread rows, manager thread rows, project rows, ellipsis menus, context-menu dismissal, and Escape close behavior.

Validation

• pnpm exec turbo run test --filter=@bb/app --force -- src/components/sidebar/ThreadRow.test.tsx src/components/sidebar/ProjectRow.test.tsx passed: 2 files, 21 tests.
• pnpm exec turbo run typecheck --filter=@bb/app --force passed.
• pnpm exec turbo run lint --filter=@bb/app --force passed.

[SawyerHood]

Updated for the follow-up feedback:

• Thread row right-click now uses Radix ContextMenu so the menu opens at the pointer location instead of the ellipsis trigger.
• Project rows now support the same right-click behavior using the existing project actions menu items/handlers.
• Dropdown and context-menu surfaces share their menu item content to keep actions structurally in sync.

Validation rerun:

• pnpm exec turbo run test --filter=@bb/app --force -- src/components/sidebar/ThreadRow.test.tsx src/components/sidebar/ProjectRow.test.tsx
• pnpm exec turbo run typecheck --filter=@bb/app --force
• pnpm exec turbo run lint --filter=@bb/app --force

[SawyerHood]

Updated this PR for the click-dismiss follow-up.

Changes:

• Context-menu action clicks now use Radix's default close behavior for thread and project right-click menus.
• Dropdown/ellipsis menu behavior remains unchanged.
• Added tests for action-click dismissal and outside-click dismissal on thread and project context menus.

Validation:

• pnpm exec turbo run test --filter=@bb/app --force -- src/components/sidebar/ThreadRow.test.tsx src/components/sidebar/ProjectRow.test.tsx passed: 2 files, 21 tests.
• pnpm exec turbo run typecheck --filter=@bb/app --force passed.
• pnpm exec turbo run lint --filter=@bb/app --force passed.