Group homepage tiles into vertically-buffered areas; add Get SimpleX App card

Split the home tiles into three areas with vertical spacing: accounts
(Users/Businesses/Bots), manage (Network/Notifications/Settings), and external
SimpleX (File upload + a new Get SimpleX App card). Move the Get SimpleX App link
out of the global footer into its own homepage card.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

manager/templates/base.html

@@ -303,8 +303,6 @@
       © <a href="https://bournemouthtechnology.co.uk" target="_blank" rel="noopener">Bournemouth Technology Ltd</a>
       <span class="sep">·</span>
       built on © <a href="https://simplex.chat" target="_blank" rel="noopener">SimpleX Network</a>
-      <span class="sep">·</span>
-      <a href="https://simplex.chat/downloads/" target="_blank" rel="noopener">Get SimpleX App</a>
     </footer>
   </main>
 </div>