fix: address Phase 1-2 audit findings

- CORS: replace permissive() with configurable whitelist (default.toml)
- Auth store: synchronously restore state at creation to eliminate
  flash-of-login-page on refresh
- MainLayout: menu highlight now tracks current route via useLocation
- Add extractErrorMessage() utility to reduce repeated error parsing
- Fix all clippy warnings across 4 crates (erp-auth, erp-config,
  erp-workflow, erp-message): remove unnecessary casts, use div_ceil,
  collapse nested ifs, reduce function arguments with DTOs

crates/erp-workflow/src/handler/instance_handler.rs

@@ -1,6 +1,7 @@
 use axum::Extension;
 use axum::extract::{FromRef, Path, Query, State};
 use axum::response::Json;
+use validator::Validate;
 
 use erp_core::error::AppError;
 use erp_core::rbac::require_permission;
@@ -22,6 +23,7 @@ where
     S: Clone + Send + Sync + 'static,
 {
     require_permission(&ctx, "workflow:start")?;
+    req.validate().map_err(|e| AppError::Validation(e.to_string()))?;
 
     let resp = InstanceService::start(
         ctx.tenant_id,
@@ -52,7 +54,7 @@ where
 
     let page = pagination.page.unwrap_or(1);
     let page_size = pagination.limit();
-    let total_pages = (total + page_size - 1) / page_size;
+    let total_pages = total.div_ceil(page_size);
 
     Ok(Json(ApiResponse::ok(PaginatedResponse {
         data: instances,