feat(core): add audit logging to all mutation operations

Create audit_log SeaORM entity and audit_service::record() helper.
Integrate audit recording into 35 mutation endpoints across all modules:
- erp-auth: user/role/organization/department/position CRUD (15 actions)
- erp-config: dictionary/menu/setting/numbering_rule CRUD (15 actions)
- erp-workflow: definition/instance/task operations (8 actions)
- erp-message: send/system/mark_read/delete (5 actions)

Uses fire-and-forget pattern — audit failures logged but non-blocking.

crates/erp-auth/src/service/dept_service.rs

@@ -8,6 +8,8 @@ use crate::dto::{CreateDepartmentReq, DepartmentResp, UpdateDepartmentReq};
 use crate::entity::department;
 use crate::entity::organization;
 use crate::error::{AuthError, AuthResult};
+use erp_core::audit::AuditLog;
+use erp_core::audit_service;
 use erp_core::error::check_version;
 use erp_core::events::EventBus;
 
@@ -124,6 +126,13 @@ impl DeptService {
             serde_json::json!({ "dept_id": id, "org_id": org_id, "name": req.name }),
         ));
 
+        audit_service::record(
+            AuditLog::new(tenant_id, Some(operator_id), "department.create", "department")
+                .with_resource_id(id),
+            db,
+        )
+        .await;
+
         Ok(DepartmentResp {
             id,
             org_id,
@@ -195,6 +204,13 @@ impl DeptService {
             .await
             .map_err(|e| AuthError::Validation(e.to_string()))?;
 
+        audit_service::record(
+            AuditLog::new(tenant_id, Some(operator_id), "department.update", "department")
+                .with_resource_id(id),
+            db,
+        )
+        .await;
+
         Ok(DepartmentResp {
             id: updated.id,
             org_id: updated.org_id,
@@ -256,6 +272,14 @@ impl DeptService {
             tenant_id,
             serde_json::json!({ "dept_id": id }),
         ));
+
+        audit_service::record(
+            AuditLog::new(tenant_id, Some(operator_id), "department.delete", "department")
+                .with_resource_id(id),
+            db,
+        )
+        .await;
+
         Ok(())
     }
 }