fix: rewrite HoverBorderGradient with CSS rotate instead of framer-motion

Replace framer-motion gradient interpolation (buggy in TG WebView) with
pure CSS conic-gradient + transform:rotate() keyframe animation.
Transform animations are GPU-accelerated and reliable everywhere.

tailwind.config.js

@@ -173,8 +173,13 @@ export default {
         'move-horizontal': 'moveHorizontal 40s ease infinite',
         'move-in-circle-fast': 'moveInCircle 20s ease infinite',
         'spotlight-ace': 'spotlightAce 2s ease 0.75s 1 forwards',
+        'border-spin': 'borderSpin 3s linear infinite',
       },
       keyframes: {
+        borderSpin: {
+          '0%': { transform: 'rotate(0deg)' },
+          '100%': { transform: 'rotate(360deg)' },
+        },
         fadeIn: {
           '0%': { opacity: '0' },
           '100%': { opacity: '1' },