refactor(api): resolve the backend URL in one place

VITE_BASE_API_URL with a localhost:3001/api fallback was re-derived in six
files across libs/api, libs/auth, the portal and the backoffice — and a seventh
site (UserManagementPage) read the env raw with no fallback at all, handing the
IAM user-management app an undefined apiUrl whenever no .env was present.

BASE_API_URL in base-query-with-reauth.ts is now the single definition,
exported from @ema-platform/api; every other site imports it. Trims the env
value and treats blank as unset, matching how the backend reads its own keys.

apps/backoffice/src/app/features/certificate-designer/config/designer.ts

@@ -1,9 +1,9 @@
 import type { Bilingual, LicenseCategory, LicenseTemplate, LicenseType } from '@ema-platform/api';
 
+import { BASE_API_URL } from '@ema-platform/api';
+
 /** Same resolution — and same fallback — the shared RTK Query baseQuery uses. */
-export const API_BASE_URL =
-  (import.meta as { env?: Record<string, string> }).env?.['VITE_BASE_API_URL'] ??
-  'http://localhost:3001/api';
+export const API_BASE_URL = BASE_API_URL;
 
 export const STATUS_COLOR: Record<LicenseTemplate['status'], string> = {
   DRAFT: 'gray',

apps/backoffice/src/app/features/user-management/UserManagementPage.tsx

@@ -3,6 +3,7 @@ import { useCallback, useEffect, useRef } from 'react';
 import { createRoot, type Root } from 'react-dom/client';
 import { useNavigate } from 'react-router-dom';
 import { UserManagementApp } from '@tria-plc/iamui';
+import { BASE_API_URL } from '@ema-platform/api';
 import type { DesignConfig, UserManagementSessionOptions } from '@tria-plc/iamui';
 import '@tria-plc/iamui/style.css';
 
@@ -99,7 +100,7 @@ const UM_CONFIG: DesignConfig = {
 
 const UM_RUNTIME = {
   basename: '/um',
-  apiUrl: import.meta.env.VITE_BASE_API_URL,
+  apiUrl: BASE_API_URL,
 };
 
 const buttonStyle: React.CSSProperties = {