chore: cursor-blink on empty-state placeholders

Adds the cursor-blink class to "no X" / "select a Y" placeholders across
core (calendar popup, board preview, search preview, detail split, notifs)
and plugins (chat, email, gitea, slideshow). Visual consistency with the
rest of the pixel-font UI.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

public/js/modules/notifications.js

@@ -148,7 +148,7 @@ function renderStream() {
     const all = getAllItems();
 
     if (!all.length) {
-        stream.innerHTML = '<div class="text-xs text-t-dim font-pixel text-center py-4">no notifications</div>';
+        stream.innerHTML = '<div class="text-xs text-t-dim font-pixel text-center py-4 cursor-blink">no notifications</div>';
         return;
     }