This change ensures the 'Explore' link is visible in the sidebar when the user is logged in, and hidden when logged out, consistent with other authenticated routes like 'For You' and 'Subscriptions'.
- Updated `js/app.js` to handle `exploreLink` visibility in `applyAuthenticatedUiState` and `applyLoggedOutUiState`.
- Initialized `exploreLink` property in `js/ui/applicationBootstrap.js`.
- Updated `tests/app/hydrate-sidebar-navigation.test.mjs` to verify the behavior.
- Add `tests/services/link-preview-service.test.mjs`: Tests for caching, fetching, and TTL logic using `fake-indexeddb` and `jsdom`.
- Add `tests/nostr/session-actor.test.mjs`: Tests for encryption/decryption and persistence of session actor.
- Refactor `tests/app/similar-content.test.mjs`: Update to test `SimilarContentController` directly, fixing regression caused by architectural changes.
- Ensure tests are self-contained with necessary polyfills (IndexedDB, LocalStorage).