Aligns terminology with standard UI conventions. Renames props,
state, handlers, aria-labels, test descriptions, and the test file.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Move panel view state, fold/pin state, isWideDesktop media query,
and all related handlers into a dedicated hook, reducing App.tsx
by ~80 lines of state management boilerplate.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>