feat: 添加用户关注功能

- 新增 Follow 表和 User.bio 字段 (Prisma schema)
- 创建 follow 模块 (action-service-repository)
- 新增 FollowButton/FollowStats/UserList 组件
- 用户页面显示 bio、粉丝/关注数、关注按钮
- 新增 /users/[username]/followers 和 following 页面
- 添加 en-US/zh-CN i18n 翻译

⚠️ 需要运行: prisma migrate dev --name add_follow_and_bio

src/app/(auth)/users/[username]/followers/page.tsx

@@ -0,0 +1,44 @@
+import { notFound } from "next/navigation";
+import { getTranslations } from "next-intl/server";
+import { PageLayout } from "@/components/ui/PageLayout";
+import { UserList } from "@/components/follow/UserList";
+import { actionGetUserProfileByUsername } from "@/modules/auth/auth-action";
+import { actionGetFollowers } from "@/modules/follow/follow-action";
+
+interface FollowersPageProps {
+  params: Promise<{ username: string }>;
+}
+
+export default async function FollowersPage({ params }: FollowersPageProps) {
+  const { username } = await params;
+  const t = await getTranslations("follow");
+
+  const userResult = await actionGetUserProfileByUsername({ username });
+
+  if (!userResult.success || !userResult.data) {
+    notFound();
+  }
+
+  const user = userResult.data;
+
+  const followersResult = await actionGetFollowers({
+    userId: user.id,
+    page: 1,
+    limit: 50,
+  });
+
+  const followers = followersResult.success && followersResult.data
+    ? followersResult.data.followers.map((f) => f.user)
+    : [];
+
+  return (
+    <PageLayout>
+      <div className="bg-white rounded-lg shadow-md p-6">
+        <h1 className="text-2xl font-bold text-gray-800 mb-6">
+          {t("followersOf", { username: user.displayUsername || user.username || "User" })}
+        </h1>
+        <UserList users={followers} emptyMessage={t("noFollowers")} />
+      </div>
+    </PageLayout>
+  );
+}