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-message/src/service/template_service.rs

@@ -113,3 +113,81 @@ impl TemplateService {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn render_replaces_single_variable() {
+        let mut vars = std::collections::HashMap::new();
+        vars.insert("name".to_string(), "张三".to_string());
+        let result = TemplateService::render("您好，{{name}}", &vars);
+        assert_eq!(result, "您好，张三");
+    }
+
+    #[test]
+    fn render_replaces_multiple_variables() {
+        let mut vars = std::collections::HashMap::new();
+        vars.insert("name".to_string(), "李四".to_string());
+        vars.insert("code".to_string(), "ORD-001".to_string());
+        let result = TemplateService::render("{{name}}，您的订单 {{code}} 已发货", &vars);
+        assert_eq!(result, "李四，您的订单 ORD-001 已发货");
+    }
+
+    #[test]
+    fn render_no_variables_returns_original() {
+        let vars = std::collections::HashMap::new();
+        let result = TemplateService::render("没有变量的模板", &vars);
+        assert_eq!(result, "没有变量的模板");
+    }
+
+    #[test]
+    fn render_missing_variable_leaves_placeholder() {
+        let vars = std::collections::HashMap::new();
+        let result = TemplateService::render("您好，{{name}}", &vars);
+        assert_eq!(result, "您好，{{name}}");
+    }
+
+    #[test]
+    fn render_same_variable_multiple_times() {
+        let mut vars = std::collections::HashMap::new();
+        vars.insert("user".to_string(), "王五".to_string());
+        let result = TemplateService::render("{{user}} 你好，{{user}} 的订单已确认", &vars);
+        assert_eq!(result, "王五 你好，王五 的订单已确认");
+    }
+
+    #[test]
+    fn render_empty_template() {
+        let mut vars = std::collections::HashMap::new();
+        vars.insert("name".to_string(), "test".to_string());
+        let result = TemplateService::render("", &vars);
+        assert_eq!(result, "");
+    }
+
+    #[test]
+    fn render_empty_variable_value() {
+        let mut vars = std::collections::HashMap::new();
+        vars.insert("name".to_string(), "".to_string());
+        let result = TemplateService::render("您好，{{name}}！", &vars);
+        assert_eq!(result, "您好，！");
+    }
+
+    #[test]
+    fn render_adjacent_variables() {
+        let mut vars = std::collections::HashMap::new();
+        vars.insert("a".to_string(), "1".to_string());
+        vars.insert("b".to_string(), "2".to_string());
+        let result = TemplateService::render("{{a}}{{b}}", &vars);
+        assert_eq!(result, "12");
+    }
+
+    #[test]
+    fn render_extra_variables_not_in_template_are_ignored() {
+        let mut vars = std::collections::HashMap::new();
+        vars.insert("name".to_string(), "赵六".to_string());
+        vars.insert("unused".to_string(), "ignore".to_string());
+        let result = TemplateService::render("你好 {{name}}", &vars);
+        assert_eq!(result, "你好 赵六");
+    }
+}