fix: add vitest.config.ts to eslint allowDefaultProject, revert tsconfig include

vitest.config.ts is not under apps/gateway/src (rootDir), so including
it in tsconfig.json broke the build. Instead, add it to the
eslint allowDefaultProject list so the typescript-eslint parser can
lint it without being covered by the project tsconfig.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/gateway/tsconfig.json

@@ -8,6 +8,6 @@
     "module": "NodeNext",
     "moduleResolution": "NodeNext"
   },
-  "include": ["src/**/*", "vitest.config.ts"],
+  "include": ["src/**/*"],
   "exclude": ["node_modules", "dist"]
 }

eslint.config.mjs

@@ -27,6 +27,7 @@ export default tseslint.config(
             'apps/web/e2e/*.ts',
             'apps/web/e2e/helpers/*.ts',
             'apps/web/playwright.config.ts',
+            'apps/gateway/vitest.config.ts',
             'packages/mosaic/__tests__/*.ts',
           ],
         },