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/email/email.html

@@ -79,7 +79,7 @@
                 <div id="email-body-empty" class="flex items-center justify-center flex-1 text-t-dim text-xs font-pixel">
                     <div class="text-center">
                         <i class="ph ph-envelope-open text-3xl mb-2 block"></i>
-                        select a message
+                        <span class="cursor-blink">select a message</span>
                     </div>
                 </div>
                 <div id="email-body" class="hidden flex flex-col flex-1 min-h-0">

public/plugins/email/email.js

@@ -441,7 +441,7 @@ function gotoNextPage() {
 function renderMessageList() {
     const list = $('email-list');
     if (!currentMessages.length) {
-        list.innerHTML = '<div class="p-4 text-xs text-t-dim italic">no messages</div>';
+        list.innerHTML = '<div class="p-4 text-xs text-t-dim italic cursor-blink">no messages</div>';
         renderSelectionBar();
         renderSpamToolbar();
         return;