Let admins create and edit roles from the dashboard (Task #82)

What changed:
- Added an `is_system` column to the `roles` table (default 0). The
  built-in roles (admin, user, order_receiver) are flagged as system roles
  in the seed and via a one-off UPDATE on the existing dev DB.
- Created a new `/api/roles` route module with admin-guarded endpoints:
    - POST /api/roles – create a role (validates name format, rejects duplicates).
    - PATCH /api/roles/:id – update bilingual descriptions; name is immutable.
    - DELETE /api/roles/:id – returns 400 for system roles (also defended
      by name allowlist), 409 with userCount/groupCount when in use, 204 on
      success. Cleans up role_permissions in a transaction.
  GET /api/roles was moved out of groups.ts into the new module.
- OpenAPI updated with createRole / updateRole / deleteRole operations,
  isSystem on the Role schema, and CreateRoleBody / UpdateRoleBody /
  RoleDeletionConflict schemas. Regenerated api-zod and api-client-react.
- Added a "Roles" item under the User Management nav group in the admin
  dashboard, plus a new RolesPanel with search, create dialog, edit dialog
  (description-only), and delete dialog with conflict messaging.
- Bilingual translations added in en.json and ar.json (admin.nav.roles +
  admin.roles.*).

Notes / deviations:
- Also marked `order_receiver` as a system role since it is seeded by the
  system and required by the orders feature, even though the task brief
  only called out admin and user.
- Verified end-to-end via the testing skill: list, create, edit, delete,
  duplicate-name validation, and protection of system roles all work.

Replit-Task-Id: b1187555-be09-4687-a9ae-83b123d908bd

scripts/src/seed.ts

@@ -23,13 +23,13 @@ async function main() {
   // Create roles
   const [adminRole] = await db
     .insert(rolesTable)
-    .values({ name: "admin", descriptionAr: "مدير النظام", descriptionEn: "System Administrator" })
+    .values({ name: "admin", descriptionAr: "مدير النظام", descriptionEn: "System Administrator", isSystem: 1 })
     .onConflictDoNothing()
     .returning();
 
   const [userRole] = await db
     .insert(rolesTable)
-    .values({ name: "user", descriptionAr: "مستخدم عادي", descriptionEn: "Regular User" })
+    .values({ name: "user", descriptionAr: "مستخدم عادي", descriptionEn: "Regular User", isSystem: 1 })
     .onConflictDoNothing()
     .returning();
 
@@ -56,6 +56,7 @@ async function main() {
       name: "order_receiver",
       descriptionAr: "مستلم الطلبات",
       descriptionEn: "Order Receiver",
+      isSystem: 1,
     })
     .onConflictDoNothing()
     .returning();