feat: enhance mobile call page with animated ripple effect

Added a new animation for the "开始通话" button on the mobile call page, providing a visual ripple effect to improve user experience. Adjusted layout for better clarity and responsiveness.

frontend/src/app/globals.css

@@ -271,4 +271,31 @@
       transparent
     );
   }
+
+  /* 手机通话页「开始通话」引导光晕：柔和向外扩散的涟漪环 */
+  @keyframes mobile-call-ripple {
+    0% {
+      transform: scale(1);
+      opacity: 0.55;
+    }
+    100% {
+      transform: scale(1.85);
+      opacity: 0;
+    }
+  }
+
+  .mobile-call-ripple {
+    animation: mobile-call-ripple 2.4s cubic-bezier(0.22, 1, 0.36, 1) infinite;
+  }
+
+  .mobile-call-ripple-delay {
+    animation-delay: 1.2s;
+  }
+
+  @media (prefers-reduced-motion: reduce) {
+    .mobile-call-ripple,
+    .mobile-call-ripple-delay {
+      animation: none;
+    }
+  }
 }