Align sidebar + homepage groups; flatten Relays (drop dropdown); move Notifications to system group

Both the sidebar and the homepage now share the same logical groups:
accounts (Users/Businesses/Bots/File Upload), relays (Chat/File/Message Relay),
system (Network/Notifications/Settings), external (Get App). Relays is now its
own flat divider-separated section in the sidebar instead of a collapsible
dropdown; remove the dropdown CSS/JS. Move Notifications into the system group
on the homepage cards.

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

manager/templates/home.html

@@ -44,10 +44,6 @@
     <span class="t-ico">🤖</span>
     <span class="t-title">Bots</span>
   </a>
-  <a class="tile" href="/notifications">
-    <span class="t-ico">🔔</span>
-    <span class="t-title">Notifications</span>
-  </a>
   <a class="tile" href="https://simplex.chat/file/" target="_blank" rel="noopener">
     <span class="t-ico">📁</span>
     <span class="t-title">File Upload</span>
@@ -70,12 +66,16 @@
   </a>
 </div>
 
-<!-- Area 2: manage -->
+<!-- Area 3: system -->
 <div class="tiles">
   <a class="tile" href="/network">
     <span class="t-ico">📡</span>
     <span class="t-title">Network</span>
   </a>
+  <a class="tile" href="/notifications">
+    <span class="t-ico">🔔</span>
+    <span class="t-title">Notifications</span>
+  </a>
   <a class="tile" href="/settings">
     <span class="t-ico">⚙️</span>
     <span class="t-title">Settings</span>