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/modules/follow/follow-repository-dto.ts

@@ -0,0 +1,51 @@
+export type RepoInputCreateFollow = {
+  followerId: string;
+  followingId: string;
+};
+
+export type RepoInputDeleteFollow = {
+  followerId: string;
+  followingId: string;
+};
+
+export type RepoInputCheckFollow = {
+  followerId: string;
+  followingId: string;
+};
+
+export type RepoInputGetFollowers = {
+  userId: string;
+  page?: number;
+  limit?: number;
+};
+
+export type RepoInputGetFollowing = {
+  userId: string;
+  page?: number;
+  limit?: number;
+};
+
+export type RepoOutputFollowUser = {
+  id: string;
+  followerId: string;
+  followingId: string;
+  createdAt: Date;
+};
+
+export type RepoOutputFollowWithUser = {
+  id: string;
+  followerId: string;
+  followingId: string;
+  createdAt: Date;
+  user: {
+    id: string;
+    username: string | null;
+    displayUsername: string | null;
+    image: string | null;
+    bio: string | null;
+  };
+};
+
+export type RepoOutputFollowerCount = number;
+export type RepoOutputFollowingCount = number;
+export type RepoOutputIsFollowing = boolean;