feat: add utoipa path annotations to all API handlers and wire OpenAPI spec

- Add #[utoipa::path] annotations to all 70+ handler functions across
  auth, config, workflow, and message modules
- Add IntoParams/ToSchema derives to Pagination, PaginatedResponse, ApiResponse
  in erp-core, and MessageQuery/TemplateQuery in erp-message
- Collect all module paths into OpenAPI spec via AuthApiDoc, ConfigApiDoc,
  WorkflowApiDoc, MessageApiDoc structs in erp-server main.rs
- Update openapi_spec handler to merge all module specs
- The /docs/openapi.json endpoint now returns complete API documentation
  with all endpoints, request/response schemas, and security requirements

crates/erp-server/src/handlers/openapi.rs

@@ -1,14 +1,18 @@
 use axum::response::Json;
 use serde_json::Value;
-use utoipa::openapi::OpenApiBuilder;
+use utoipa::OpenApi;
+
+use crate::{ApiDoc, AuthApiDoc, ConfigApiDoc, WorkflowApiDoc, MessageApiDoc};
 
 /// GET /docs/openapi.json
 ///
-/// 返回 OpenAPI 3.0 规范 JSON 文档
+/// 返回 OpenAPI 3.0 规范 JSON 文档，合并所有模块的路径和 schema。
 pub async fn openapi_spec() -> Json<Value> {
-    let mut info = utoipa::openapi::Info::new("ERP Platform API", env!("CARGO_PKG_VERSION"));
-    info.description = Some("ERP 平台底座 REST API 文档".to_string());
+    let mut spec = ApiDoc::openapi();
+    spec.merge(AuthApiDoc::openapi());
+    spec.merge(ConfigApiDoc::openapi());
+    spec.merge(WorkflowApiDoc::openapi());
+    spec.merge(MessageApiDoc::openapi());
 
-    let spec = OpenApiBuilder::new().info(info).build();
     Json(serde_json::to_value(spec).unwrap_or_default())
 }