Tidy homepage subtitle out; restyle sidebar collapse button

Remove the homepage tagline. Make the collapse control a proper inset pill with
a 'Collapse' label + chevron (label left, chevron right) instead of a bare
full-width row with a lone arrow; centers to just the icon when collapsed.

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

manager/templates/home.html

@@ -26,7 +26,6 @@
 {% block content %}
 <div class="home-head">
   <h1>SimpleX Manager</h1>
-  <p>Manage your SimpleX accounts, business inboxes and bots — pick a section to get started.</p>
 </div>
 
 <div class="tiles">