feat: add caching for nostr-native articles

- Add localStorage caching for kind:30023 articles (same as web articles)
- Cache TTL: 7 days
- Cache key prefix: article_cache_
- Add bypassCache parameter to fetchArticleByNaddr()
- Log cache hits and misses for debugging
- Gracefully handle storage errors

Articles are now cached locally after first fetch, making subsequent
loads instant and reducing relay queries.

.cursor/rules/highlights-nip-and-docs.mdc

@@ -1,3 +1,9 @@
 ---
-alwaysApply: true
+description: nostr highlights spec and docs
+alwaysApply: false
 ---
+
+Here's the spec for nostr-native highlights: 
+
+- https://github.com/nostr-protocol/nips/blob/master/84.md
+- https://nostrbook.dev/kinds/9802