Fix: Sidebar 'Subscriptions' link remains hidden for logged-in users

The `resolveSubscriptionsLink` method in `js/app.js` cached the sidebar DOM element (`this.subscriptionsLink`) during initialization. However, the sidebar is re-rendered dynamically, causing the cached reference to point to a detached DOM node. Consequently, `applyAuthenticatedUiState` would update the visibility of the detached element, leaving the visible sidebar unchanged.

This fix updates `resolveSubscriptionsLink` to check `this.subscriptionsLink.isConnected`. If the cached element is detached, it re-queries the DOM to retrieve the current live element, ensuring visibility updates apply correctly.

Additionally, `js/index.js` now awaits `applicationReadyPromise` before hydrating the sidebar, preventing race conditions during startup. `js/nostr/toolkit.js` was updated to support function-based subscription closers, fixing potential leaks.

js/app.js

@@ -3866,7 +3866,10 @@ class Application {
   }
 
   resolveSubscriptionsLink() {
-    if (this.subscriptionsLink instanceof HTMLElement) {
+    if (
+      this.subscriptionsLink instanceof HTMLElement &&
+      this.subscriptionsLink.isConnected
+    ) {
       return this.subscriptionsLink;
     }