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/models/identity.dart

@@ -146,6 +146,9 @@ class LocalIdentity {
 /// kontaktu poslat první zpráva. Obě pole jsou náhodná — s identitou je
 /// spojuje jen sám uživatel tím, že je sdílí ve svém odkazu.
 class PublicIdentity {
+  /// Nejvyšší délka jména z odkazu/QR — delší odkaz je vadný vstup.
+  static const maxDisplayNameLength = 64;
+
   PublicIdentity({
     required this.displayName,
     required this.identityKey,
@@ -214,7 +217,14 @@ class PublicIdentity {
           as Map<String, dynamic>;
       if (map['v'] != 2) return null;
       final identityKey = base64Decode(map['ik'] as String);
-      if (identityKey.length != 33) return null;
+      // 33 B = typový bajt 0x05 + Curve25519; jiný prefix libsignal odmítne
+      // až při první zprávě, tady ho odmítneme hned.
+      if (identityKey.length != 33 || identityKey[0] != 0x05) return null;
+      final aid = map['aid'] as String?;
+      // Relay dává 32 hex znaků; starší testovací odkazy kratší — hex a strop stačí.
+      if (aid != null && !RegExp(r'^[0-9a-f]{8,64}$').hasMatch(aid)) return null;
+      final rawName = (map['n'] as String).trim();
+      if (rawName.length > maxDisplayNameLength) return null;
       final da = map['da'] as String?;
       Uint8List? deliveryAddress;
       if (da != null) {
@@ -224,10 +234,10 @@ class PublicIdentity {
         if (deliveryAddress.length != 32) return null;
       }
       return PublicIdentity(
-        displayName: map['n'] as String,
+        displayName: rawName,
         identityKey: identityKey,
         createdAt: DateTime.parse(map['ts'] as String),
-        accountId: map['aid'] as String?,
+        accountId: aid,
         deliveryAddress: deliveryAddress,
       );
     } catch (_) {