fix: address Bugbot review #2 findings

- Invalidate integration data cache from widget interact mutations
  (downloads, dns-hole, media-requests, indexer-manager, smart-home, anchor-notes)
- Redis handler getExpiration: fetch missing tags from Redis (multi-instance coherence)
- saveItemOptions: invalidate board cache after saving
- Remove unused cacheTags.app
- Fix integration data cache comment accuracy

packages/api/src/integration-data-cache.ts

@@ -1,6 +1,6 @@
 // ponytail: module-level cache is single-instance only.
-// Multi-instance deployments (REDIS_IS_EXTERNAL=true) bypass this and rely on
-// the Redis-backed Next cache handler for cross-instance coordination.
+// Multi-instance deployments (REDIS_IS_EXTERNAL=true) bypass this entirely —
+// each request calls the upstream fetcher directly.
 const isMultiInstance = process.env.REDIS_IS_EXTERNAL === "true";
 
 interface CachedEntry<T> {