chore: upgrade Tailwind CSS to v4

- Replace @tailwind directives with @import "tailwindcss"
- Switch PostCSS plugin to @tailwindcss/postcss
- Add @theme inline block mapping CSS vars to v4 theme tokens
- Move accordion keyframes/animations to globals.css
- Remove tailwind.config.ts and tailwindcss-animate (no longer needed)
- Update components.json to clear config path

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

components.json

@@ -4,7 +4,7 @@
   "rsc": true,
   "tsx": true,
   "tailwind": {
-    "config": "tailwind.config.ts",
+    "config": "",
     "css": "app/globals.css",
     "baseColor": "zinc",
     "cssVariables": true,