style: establish visually distinct hierarchies for main categories, tool items, and tree sub-links

feat: make major sidebar navigation sections collapsible and persist their state in localStorage

style: group sidebar navigation links into clean logical sections using uppercase category headers

feat: design modern, premium global Select2 dropdown styles and integrate with dynamic options reloading across all tools

feat: redesign Audio Story Studio UI v2 - sticky timeline, char counter, waveform, improved layout

Initial commit: PUM'S TOOLKIT - AI-powered tools collection