feat: FAB 플로팅 액션 버튼 컴포넌트

src/components/FAB.jsx

@@ -0,0 +1,37 @@
+import { useIsMobile } from '../hooks/useIsMobile';
+import './FAB.css';
+
+const PlusIcon = () => (
+  <svg
+    className="fab__icon"
+    width="24"
+    height="24"
+    viewBox="0 0 24 24"
+    fill="none"
+    aria-hidden="true"
+  >
+    <path
+      d="M12 5v14M5 12h14"
+      stroke="currentColor"
+      strokeWidth="2"
+      strokeLinecap="round"
+    />
+  </svg>
+);
+
+export default function FAB({ onClick, icon, label = '액션', className = '' }) {
+  const isMobile = useIsMobile();
+
+  if (!isMobile) return null;
+
+  return (
+    <button
+      type="button"
+      className={`fab ${className}`}
+      onClick={onClick}
+      aria-label={label}
+    >
+      {icon ?? <PlusIcon />}
+    </button>
+  );
+}