fix(apk): 2 min de grace apres une copie, retour automatique decoche par defaut

Android ne laisse pas choisir l'app qui passe devant : moveTaskToBack
ramenait souvent l'ecran d'accueil. Le coffre se reverrouillait aussi
apres 30 s, avant qu'on revienne chercher le mot de passe.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

android-client/web/app.html

@@ -631,11 +631,13 @@
          "Diagnostics" au-dessus de rien. -->
     <h2>Copy and search</h2>
     <label class="opt"><input type="checkbox" id="sBack">
-      Go back to the previous app after copying</label>
+      Hide Vault after copying (may show the home screen)</label>
     <label class="opt"><input type="checkbox" id="sKbd">
       Open the keyboard on the search when the vault opens</label>
-    <div class="note">Copy, and you are back in the browser or app you came
-      from, ready to paste. Come back and the search is ready to type.</div>
+    <div class="note">To jump back to the app you came from, use Android's own
+      gesture: swipe along the bottom bar, or tap the recent-apps button twice.
+      After a copy the vault stays open for 2 minutes in the background, time
+      to paste the username and come back for the password.</div>
 
     <h2 id="sDiagH">Diagnostics</h2>
     <button class="btn wide" id="sLog">Show the log</button>