fix(app): accept incoming calls, restore from recovery phrase, duress session isolation, message loss

Calls: `call` was missing from the known content types, so every offer was
acknowledged and dropped; the call screen column now fills the width (the
avatar jumped left after hang-up); a ring started from a push ends after
12 s when no offer arrives; STUN fallback when no TURN credentials.
Registration: X-Sepot-Identity-Proof lets a new device reclaim an existing
identity; retry backs off from 30 s to 10 min and exposes a conflict flag.
Prekeys: PrekeysLow triggers a batch of 50 one-time prekeys via POST
/v1/keys; the signed prekey rotates weekly, the Kyber prekey monthly.
Messaging: crypto operations run serially (concurrent encrypts derived the
same message key); stop() waits for in-flight deliveries (auto-lock between
decrypt and persist lost messages); disappearing-message cleanup no longer
overwrites fresh messages; a push wake-up reconnects stale connections; the
outbox carries polls and mentions; length limits on wire input.
Storage: a duress session never exposes the real identity or phrase, does
not start networking and cannot touch the keystore; deleting data in a
duress session leaves the real account alone; PIN guessing is throttled
(5 misses, then 30 s doubling up to 15 min); the duress blob shares the salt
so unlock time does not reveal which PIN was entered; iOS keychain items are
this-device only; biometrics are biometric-only; screen security defaults
to on and is applied after unlock; tapjacking filter in MainActivity.
Tests: content types, shared-salt unwrap, duress isolation.

app/lib/providers/messaging_provider.dart

@@ -55,6 +55,9 @@ final messagingStartProvider = FutureProvider<void>((ref) async {
   // se provider invaliduje (viz unlock cesty) a spustí start znovu.
   final storage = ref.read(storageProvider);
   if (!storage.isUnlocked) return;
+  // Nátlaková relace: žádná síť. Messaging by se registroval skutečným
+  // identity klíčem (409 každých 30 s = důkaz pro pozorovatele sítě).
+  if (storage.isDecoyMode) return;
 
   final service = ref.read(messagingServiceProvider);
   if (service.isStarted) return;