test: add 149 unit tests across core, auth, config, message crates

Test coverage increased from ~34 to 183 tests (zero failures):

- erp-core (21): version check, pagination, API response, error mapping
- erp-auth (39): org tree building, DTO validation, error conversion,
  password hashing, user model mapping
- erp-config (57): DTO validation, numbering reset logic, menu tree
  building, error conversion. Fixed BatchSaveMenusReq nested validation
- erp-message (50): DTO validation, template rendering, query defaults,
  error conversion
- erp-workflow (16): unchanged (parser + expression tests)

All tests are pure unit tests requiring no database.

crates/erp-auth/src/dto.rs

@@ -209,3 +209,183 @@ pub struct UpdatePositionReq {
     pub sort_order: Option<i32>,
     pub version: i32,
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use validator::Validate;
+
+    #[test]
+    fn login_req_valid() {
+        let req = LoginReq {
+            username: "admin".to_string(),
+            password: "password123".to_string(),
+        };
+        assert!(req.validate().is_ok());
+    }
+
+    #[test]
+    fn login_req_empty_username_fails() {
+        let req = LoginReq {
+            username: "".to_string(),
+            password: "password123".to_string(),
+        };
+        let result = req.validate();
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn login_req_empty_password_fails() {
+        let req = LoginReq {
+            username: "admin".to_string(),
+            password: "".to_string(),
+        };
+        assert!(req.validate().is_err());
+    }
+
+    #[test]
+    fn create_user_req_valid() {
+        let req = CreateUserReq {
+            username: "alice".to_string(),
+            password: "secret123".to_string(),
+            email: Some("alice@example.com".to_string()),
+            phone: None,
+            display_name: Some("Alice".to_string()),
+        };
+        assert!(req.validate().is_ok());
+    }
+
+    #[test]
+    fn create_user_req_short_password_fails() {
+        let req = CreateUserReq {
+            username: "bob".to_string(),
+            password: "12345".to_string(), // min 6
+            email: None,
+            phone: None,
+            display_name: None,
+        };
+        assert!(req.validate().is_err());
+    }
+
+    #[test]
+    fn create_user_req_empty_username_fails() {
+        let req = CreateUserReq {
+            username: "".to_string(),
+            password: "secret123".to_string(),
+            email: None,
+            phone: None,
+            display_name: None,
+        };
+        assert!(req.validate().is_err());
+    }
+
+    #[test]
+    fn create_user_req_invalid_email_fails() {
+        let req = CreateUserReq {
+            username: "charlie".to_string(),
+            password: "secret123".to_string(),
+            email: Some("not-an-email".to_string()),
+            phone: None,
+            display_name: None,
+        };
+        assert!(req.validate().is_err());
+    }
+
+    #[test]
+    fn create_user_req_long_username_fails() {
+        let req = CreateUserReq {
+            username: "a".repeat(51), // max 50
+            password: "secret123".to_string(),
+            email: None,
+            phone: None,
+            display_name: None,
+        };
+        assert!(req.validate().is_err());
+    }
+
+    #[test]
+    fn create_role_req_valid() {
+        let req = CreateRoleReq {
+            name: "管理员".to_string(),
+            code: "admin".to_string(),
+            description: Some("系统管理员".to_string()),
+        };
+        assert!(req.validate().is_ok());
+    }
+
+    #[test]
+    fn create_role_req_empty_name_fails() {
+        let req = CreateRoleReq {
+            name: "".to_string(),
+            code: "admin".to_string(),
+            description: None,
+        };
+        assert!(req.validate().is_err());
+    }
+
+    #[test]
+    fn create_role_req_empty_code_fails() {
+        let req = CreateRoleReq {
+            name: "管理员".to_string(),
+            code: "".to_string(),
+            description: None,
+        };
+        assert!(req.validate().is_err());
+    }
+
+    #[test]
+    fn create_org_req_valid() {
+        let req = CreateOrganizationReq {
+            name: "总部".to_string(),
+            code: Some("HQ".to_string()),
+            parent_id: None,
+            sort_order: Some(0),
+        };
+        assert!(req.validate().is_ok());
+    }
+
+    #[test]
+    fn create_org_req_empty_name_fails() {
+        let req = CreateOrganizationReq {
+            name: "".to_string(),
+            code: None,
+            parent_id: None,
+            sort_order: None,
+        };
+        assert!(req.validate().is_err());
+    }
+
+    #[test]
+    fn create_dept_req_valid() {
+        let req = CreateDepartmentReq {
+            name: "技术部".to_string(),
+            code: Some("TECH".to_string()),
+            parent_id: None,
+            manager_id: None,
+            sort_order: Some(1),
+        };
+        assert!(req.validate().is_ok());
+    }
+
+    #[test]
+    fn create_position_req_valid() {
+        let req = CreatePositionReq {
+            name: "高级工程师".to_string(),
+            code: Some("SENIOR".to_string()),
+            level: Some(3),
+            sort_order: None,
+        };
+        assert!(req.validate().is_ok());
+    }
+
+    #[test]
+    fn create_position_req_empty_name_fails() {
+        let req = CreatePositionReq {
+            name: "".to_string(),
+            code: None,
+            level: None,
+            sort_order: None,
+        };
+        assert!(req.validate().is_err());
+    }
+}