Expand App edge interaction coverage

[benvinegar]

Summary

• add App interaction coverage for filter-driven reselection, menu wrap-around, and sidebar toggles
• extract sidebar width clamp math into a small UI helper that is directly testable
• add helper coverage for the sidebar drag-width math

Testing

• bun test test/app-interactions.test.tsx test/ui-lib.test.ts
• bun run typecheck
• bun test --coverage