feat: PM panel under ERP shell + project-supervisor role

- /panel/pm: the PM app (served on the same origin under /pm) is embedded as
  a full-height iframe; supervisors are funneled there from every route,
  ERP MobileTabBar hidden on that route
- Panels menu: «مدیریت پروژه (PM)» is an internal route (admin/pm/supervisor
  only — procurement managers do not see it); PM link is no longer external
- New system role 'supervisor' (user_role enum): label in users router,
  allowed in UserRoleUpdate schema, deny-by-default on all ERP routers;
  admin panel can grant/revoke it alongside procurement manager
- Removed the obsolete VITE_PM_URL build plumbing (same-origin now)

frontend/src/store/auth.ts

@@ -14,7 +14,7 @@ export interface AuthUser {
   first_name: string;
   last_name: string;
   phone: string | null;
-  role: "pm" | "procurement_manager" | "admin" | null;
+  role: "pm" | "procurement_manager" | "admin" | "supervisor" | null;
   role_label: string | null;
   project_id: string | null; // پروژه‌ی فعال (PM) — با سوییچر عوض می‌شود
   project_name: string | null;