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

prisma/migrations/20260310065727_add_follow_and_bio/migration.sql

@@ -0,0 +1,27 @@
+-- AlterTable
+ALTER TABLE "user" ADD COLUMN     "bio" TEXT;
+
+-- CreateTable
+CREATE TABLE "follows" (
+    "id" TEXT NOT NULL,
+    "follower_id" TEXT NOT NULL,
+    "following_id" TEXT NOT NULL,
+    "created_at" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "follows_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE INDEX "follows_follower_id_idx" ON "follows"("follower_id");
+
+-- CreateIndex
+CREATE INDEX "follows_following_id_idx" ON "follows"("following_id");
+
+-- CreateIndex
+CREATE UNIQUE INDEX "follows_follower_id_following_id_key" ON "follows"("follower_id", "following_id");
+
+-- AddForeignKey
+ALTER TABLE "follows" ADD CONSTRAINT "follows_follower_id_fkey" FOREIGN KEY ("follower_id") REFERENCES "user"("id") ON DELETE CASCADE ON UPDATE CASCADE;
+
+-- AddForeignKey
+ALTER TABLE "follows" ADD CONSTRAINT "follows_following_id_fkey" FOREIGN KEY ("following_id") REFERENCES "user"("id") ON DELETE CASCADE ON UPDATE CASCADE;