refactor(library): use native select elements in filter popover

Commit notes

- Replace accordion-style filter sections with native <select> elements - Add custom .filter-select styling for dark theme consistency - Include proper labels for accessibility - Simplify handlers to work with native select change events - Maintain all existing filter functionality (tags, mood, BPM, key, sort) - Keep sort direction toggle button alongside sort select

Co-authored-by: armin.naimi <[email redacted]>