Add local settings management

Add cellular-first ntfy delivery with WiFi fallback and safe SIM868 HTTP header framing.

Co-authored-by: Copilot <[email protected]>

templates/base.html

@@ -41,6 +41,11 @@
                             <i class="fas fa-exclamation-triangle"></i><span>DTC</span>
                         </a>
                     </li>
+                    <li class="nav-item">
+                        <a class="nav-link{% if request.endpoint == 'settings' %} active{% endif %}" href="{{ url_for('settings') }}">
+                            <i class="fas fa-cog"></i><span>Settings</span>
+                        </a>
+                    </li>
                 </ul>
                 <div class="text-center d-none d-md-inline">
                     <button class="btn rounded-circle border-0" id="sidebarToggle" type="button" aria-label="Toggle sidebar"></button>