fix(mcp): honor configured OAuth base URL

apps/nextjs/src/env.ts

@@ -1,7 +1,9 @@
 import { createBooleanSchema, createEnv } from "@homarr/core/infrastructure/env";
+import { z } from "zod/v4";
 
 export const env = createEnv({
   server: {
+    BASE_URL: z.string().url().optional(),
     UNSAFE_ENABLE_MOCK_INTEGRATION: createBooleanSchema(false),
     DEMO_MODE: createBooleanSchema(false),
     DEMO_READ_ONLY: createBooleanSchema(true),