R-729 + R-545: the household can remove its own off-site target („Távoli mentési cél törlése")

POST /backup/offbox/clear (reveal-then-confirm) forgets the target and deletes ssh_key + known_hosts;
nothing on the target is touched. repo_password is kept whenever anything could depend on it (hub
sealed package — the R-241 rule; escrowed; a successful run; snapshots) and deleted only otherwise.
Refused for the Felhom tier (rclone-pinned), while the single-flight is held, and while an
abandonment countdown runs. i18n parity fixtures of backups_remote gain the additive block only.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

controller/internal/web/testdata/i18n_parity/backups_remote_incomplete.html

@@ -277,6 +277,19 @@
             <button type="submit" class="btn btn-sm btn-primary" style="margin-top:.5rem">Mentés</button>
         </form>
     </details>
+    
+    
+    <div style="margin-top:.75rem" id="offbox-clear">
+        <button type="button" class="btn btn-xs btn-outline" id="offbox-clear-reveal" onclick="var c=document.getElementById('offbox-clear-confirm');c.style.display='block';this.style.display='none'">Távoli mentési cél törlése</button>
+        <div id="offbox-clear-confirm" style="display:none;margin-top:.6rem">
+            <p class="form-hint" style="margin:0 0 .5rem">A gép elfelejti ezt a távoli mentési célt, és törli a hozzá tartozó SSH kulcsot. A célgépen lévő mentésekhez nem nyúl: azok ott maradnak, ahol vannak. Ezután nem fut távoli mentés, amíg új célt nem állítasz be.</p>
+            <form method="POST" action="/backup/offbox/clear" style="display:inline">
+                <input type="hidden" name="confirm" value="1">
+                <button type="submit" class="btn btn-sm btn-primary">Igen, töröld a célt</button>
+            </form>
+        </div>
+    </div>
+    
 </div>