feat: 完成用户微服务 gRPC 实现，包含数据库与服务启动逻辑

backend/services/user-svc/user.proto

@@ -0,0 +1,64 @@
+syntax = "proto3";
+
+package user;
+
+option go_package = "./user";
+
+message User {
+  string id = 1;
+  string name = 2;
+  string email = 3;
+  string password = 4;
+}
+
+message CreateUserRequest {
+  string name = 1;
+  string email = 2;
+  string password = 3;
+}
+
+message CreateUserResponse {
+  User user = 1;
+}
+
+message GetUserRequest {
+  string id = 1;
+}
+
+message GetUserResponse {
+  User user = 1;
+}
+
+message ListUsersRequest {
+}
+
+message ListUsersResponse {
+  repeated User users = 1;
+}
+
+message UpdateUserRequest {
+  string id = 1;
+  string name = 2;
+  string email = 3;
+  string password = 4;
+}
+
+message UpdateUserResponse {
+  User user = 1;
+}
+
+message DeleteUserRequest {
+  string id = 1;
+}
+
+message DeleteUserResponse {
+  bool success = 1;
+}
+
+service UserService {
+  rpc CreateUser(CreateUserRequest) returns (CreateUserResponse);
+  rpc GetUser(GetUserRequest) returns (GetUserResponse);
+  rpc ListUsers(ListUsersRequest) returns (ListUsersResponse);
+  rpc UpdateUser(UpdateUserRequest) returns (UpdateUserResponse);
+  rpc DeleteUser(DeleteUserRequest) returns (DeleteUserResponse);
+}