feat: Prisma 用户落库、迁移与启动环境加载

- Prisma 7 + adapter-pg；prisma.config 与 users 初始迁移\n- AppModule 挂载 PrismaModule；PrismaService 仅依赖 DATABASE_URL\n- main 入口 dotenv/config，避免 Prisma 早于 Config 读 env\n- 短信登录 upsert User；默认昵称 Chat+手机号后四位\n- README / project-solution：目录、迁移规范、用户 avatar_url 说明\n- 依赖：dotenv、@prisma/adapter-pg、pg

Made-with: Cursor

prisma/migrations/migration_lock.toml

@@ -0,0 +1,3 @@
+# Please do not edit this file manually
+# It should be added in your version-control system (e.g., Git)
+provider = "postgresql"