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/chat/chat.html

@@ -14,7 +14,7 @@
         <div id="chat-list" class="chat-list"></div>
         <div id="chat-empty" class="hidden chat-empty">
             <i class="ph ph-chats text-2xl text-t-dim mb-2"></i>
-            <p class="font-pixel text-[10px] text-t-dim">no conversations yet</p>
+            <p class="font-pixel text-[10px] text-t-dim cursor-blink">no conversations yet</p>
             <button id="chat-empty-start" class="mt-3 px-2 py-1 text-[10px] font-pixel border border-t-accent text-t-accent hover:bg-t-accent/10 transition-colors">Start chat</button>
         </div>
     </div>