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/plugins/gitea/gitea.html

@@ -73,7 +73,7 @@
                 <div id="gitea-detail-empty" class="flex items-center justify-center flex-1 text-t-dim text-xs font-pixel">
                     <div class="text-center">
                         <i class="ph ph-list-bullets text-3xl mb-2 block"></i>
-                        select an issue
+                        <span class="cursor-blink">select an issue</span>
                     </div>
                 </div>
                 <!-- ── Create issue form ── -->