Closes #254

Polish FiltersSidebar with Collapse Persistence

Summary

This PR implements collapsible filter sections in FiltersSidebar with localStorage persistence to remember collapsed states across page visits. Users can now collapse/expand each filter group (Categories, Price range, Popularity) independently, and their preferences are saved for future sessions.

Changes

src/components/FiltersSidebar.tsx

• Refactored filter sections into a reusable FilterGroup component with collapsible behavior
• Each filter group now has an expandable/collapsible header with a chevron indicator
• Uses usePersistedState hook to persist collapsed state in localStorage
• Implements proper ARIA attributes (aria-expanded, aria-controls) for accessibility
• Uses hidden attribute to hide collapsed content from screen readers

src/components/icons/ChevronIcon.tsx (new)

• New icon component for the expand/collapse chevron indicator
• Follows the existing icon pattern in the codebase (size variants, accessibility)

src/components/icons/index.tsx

• Added export for the new ChevronIcon component

src/index.css

• Added styles for .filter-group__header, .filter-group__chevron, and .filter-group__panel
• Includes hover and focus-visible states matching design-token patterns
• Reduced motion support via prefers-reduced-motion media query
• Responsive adjustments for smaller viewports (max-width: 640px)

src/state/uiPrefs.ts

• Added isSectionCollapsed(), toggleSectionCollapsed(), and setSectionCollapsed() functions for collapsed section state management

Test Files

• src/components/FiltersSidebar.test.tsx - New comprehensive tests for collapse functionality
• src/state/uiPrefs.test.ts - Tests for the uiPrefs collapse state functions

Accessibility (WCAG 2.1 AA)

• aria-expanded indicates the current state of each filter group
• aria-controls associates headers with their content panels
• hidden attribute removes collapsed content from assistive technology
• Focus styles use var(--accent) with proper contrast against both light and dark backgrounds
• prefers-reduced-motion support for users who request reduced motion

Responsive Design

The filter headers adapt to smaller screens:

• Reduced padding (10px 14px) on screens under 640px
• Smaller font size (0.9rem) on mobile viewports
• All breakpoints maintain proper touch target sizes (minimum 44px height)

API/Visible Changes

Component API (no breaking changes)

FiltersSidebar maintains the same external props interface - this is a purely visual enhancement.

localStorage Keys

• callora.filters.categories.collapsed - Categories section state (boolean)
• callora.filters.price.collapsed - Price range section state (boolean)
• callora.filters.popularity.collapsed - Popularity section state (boolean)

Test Output

✓ src/components/FiltersSidebar.test.tsx (16 tests) 966ms
✓ src/state/uiPrefs.test.ts (9 tests) 11ms

All tests pass including:

• Default expanded state verification
• localStorage persistence on toggle
• State restoration on re-render
• aria-expanded and aria-controls attribute correctness
• Independent collapse/expand of each section
• Chevron rotation animation
• Price validation error handling

Notes

The existing tests in the repository have pre-existing issues unrelated to this change:

• FiltersBottomSheet.test.tsx - missing window.matchMedia mock in jsdom
• Tabs.test.tsx - same matchMedia issue
• ApiDetailPage.tsx, ApiUsage.tsx, ApiCard.tsx - JSX syntax errors in existing code

These do not affect the functionality of the changes in this PR.