feat: pause Today during mobile Security Center (Closes #1086)

frontend/index.html

@@ -51,6 +51,10 @@
       <div><h2>Security Center</h2><p class="small muted">Investigate activity, remove untrusted access, and verify the result.</p></div>
       <button id="close-active-devices" type="button" aria-label="Close active devices">Close</button>
     </div>
+    <aside class="today-detour-interruption" id="security-center-today-detour" data-today-detour role="status" aria-live="polite" hidden>
+      <strong data-today-detour-label>Today paused</strong>
+      <button id="return-from-security-center" data-return-from-detour type="button">Return to Today</button>
+    </aside>
     <nav class="security-section-nav" aria-label="Security Center sections">
       <button id="security-section-activity" type="button">Activity</button>
       <button id="security-section-devices" type="button">Devices</button>