refactor: 提取 UserAvatar、Input、Card 三个可复用 UI 组件

- UserAvatar: 统一头像渲染（5 种尺寸），新增 resolveAvatar 工具函数，替换 SwipeDeck 和 RoomManageModal 中的重复逻辑
- Input: 统一表单输入样式（4 种尺寸 + default/purple 变体），替换 AuthModal、ProfilePage、BlindboxPage 共 12 处
- Card: 统一卡片容器样式 + 可选淡入动画和延迟，替换 ProfilePage 中 7 处重复的 motion.div

src/components/Card.tsx

@@ -0,0 +1,37 @@
+import { motion } from "framer-motion";
+import type { ReactNode } from "react";
+
+interface CardProps {
+  children: ReactNode;
+  className?: string;
+  animated?: boolean;
+  delay?: number;
+}
+
+const fadeUp = {
+  initial: { y: 10, opacity: 0 },
+  animate: { y: 0, opacity: 1 },
+} as const;
+
+export default function Card({
+  children,
+  className = "",
+  animated = false,
+  delay,
+}: CardProps) {
+  const cls = `rounded-2xl bg-surface p-4 ring-1 ring-border ${className}`;
+
+  if (animated) {
+    return (
+      <motion.div
+        className={cls}
+        {...fadeUp}
+        transition={delay ? { delay } : undefined}
+      >
+        {children}
+      </motion.div>
+    );
+  }
+
+  return <div className={cls}>{children}</div>;
+}