Refactor search animation to use Tailwind utilities

Commit notes

- Move keyframes and animation utilities to app.css - Add @utility directives: animate-search-expand, animate-search-content, transition-search - Replace component <style> block with Tailwind utility classes - Add search animation classes to reduced motion media query - Follows project's Tailwind v4 patterns with @utility directive

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