fix: address PR review findings

- Revert undici to v7.27.1 (v8 blocked by #5467 qBittorrent regression)
- Broaden cache invalidation to utils.integration.invalidate() (covers
  all integration queries, not just integration.all)
- Add invalidation to onboarding integration create path
- Harden renovate test to assert allowBuilds key exists
- Remove deprecated Vitest 4 poolOptions config
- Fix CSS typo in docs menu transition (0.s → 0.5s)
- Update renovate.json5 comment to reference allowBuilds

vitest.config.mts

@@ -9,11 +9,6 @@ export default defineConfig({
     environment: "jsdom",
     include: ["**/*.spec.ts"],
     clearMocks: true,
-    poolOptions: {
-      threads: {
-        singleThread: false,
-      },
-    },
     coverage: {
       provider: "v8",
       reporter: ["html", "json-summary", "json"],