fix type check failure in @remark42/api package

Add skipLibCheck to skip type checking of .d.ts files in node_modules,
matching the setting already used by the main remark42 app. Fixes
@types/eslint-scope vs @types/eslint type incompatibility.

frontend/packages/api/tsconfig.json

@@ -7,7 +7,8 @@
     "declaration": true,
     "isolatedModules": true,
     "forceConsistentCasingInFileNames": true,
-    "strict": true
+    "strict": true,
+    "skipLibCheck": true
   },
   "include": ["index.ts", "clients", "lib"],
   "exclude": ["tests", "coverage"]