refactor: load RBAC users from API for audit log user filter

Instead of extracting users from log entries, fetch all users
with RBAC roles via dedicated endpoint for complete user list.

src/api/rbac.ts

@@ -49,6 +49,16 @@ export interface UserRoleAssignment {
   user_telegram_id: number | null;
 }
 
+export interface AdminWithRoles {
+  user_id: number;
+  telegram_id: number | null;
+  username: string | null;
+  first_name: string | null;
+  last_name: string | null;
+  email: string | null;
+  role_names: string[];
+}
+
 export interface AssignRolePayload {
   user_id: number;
   role_id: number;
@@ -167,6 +177,13 @@ export const rbacApi = {
     return response.data;
   },
 
+  // --- RBAC Users ---
+
+  getRbacUsers: async (): Promise<AdminWithRoles[]> => {
+    const response = await apiClient.get<AdminWithRoles[]>(`${BASE}/users`);
+    return response.data;
+  },
+
   // --- Role Users ---
 
   getRoleUsers: async (roleId: number): Promise<UserRoleAssignment[]> => {