…lity

Updates CategoryFilter to accept both string and string[] for selectedCategories parameter. Maintains backward compatibility while enabling filtering by multiple categories simultaneously.

Updates state initialization, setSelectedCategory method signature, and clearFilters to work with string[] instead of string for category selection.

Updates selectedCategory state to use string[] type and initializes with empty array. Updates clearFilters to reset to empty array.

Implements multi-category selection in SearchAndFilters component:
- Adds category toggle functionality allowing multiple selections
- Displays selected categories as removable badges with X icon
- Shows count of selected categories in dropdown
- Includes 'Clear all' button when multiple categories are selected
- Adds checkmark indicator for selected items in dropdown

Adds comprehensive test coverage for multi-category filtering:
- Tests filtering with empty array
- Tests filtering with single category (both string and array)
- Tests filtering with multiple categories
- Tests cases where none of the categories match
- Adds eslint-disable comments for type assertions

Updates all test cases in AwesomeSEOApp to use string[] for category selection:
- Changes setSelectedCategory calls to pass arrays
- Updates assertions to use toEqual for array comparisons
- Ensures all tests pass with new category array type

Regenerates production bundle and CSS with multi-category selection functionality.