fix: reliable first-message send, QR routing, auto-lock recovery

Fixes reported by testers and found in an app review:

- First message right after install no longer fails. Before the app
  finished registering with the relay, the outgoing message could crash on
  a null delivery address. The profile field is now optional and the send
  path throws a clear "still connecting, try again shortly" error while
  registration completes in the background.
- The QR code and share link now appear only once the delivery address is
  ready. Previously a link generated before the first connection lacked
  routing, so the other side could not send the first message. The screen
  now shows a connecting state and reactively swaps in the QR when ready.
- Incomplete contact links are rejected on import instead of failing at
  first send, with a clear prompt to ask for a fresh link.
- Auto-lock no longer silences the app: after locking and unlocking,
  messaging is restarted (it previously stayed dead until app restart).
- Group messages are marked failed on a non-per-member send error instead
  of hanging in the "sending" state forever.
- Hardened the relay client against a rare duplicate connection when
  toggling Tor or locking mid-connect, and fromShareString now rejects a
  delivery address of the wrong length.
- Pin unifiedpush below 6.2.0 to drop the webcrypto dependency (its native
  framework lacks LC_ENCRYPTION_INFO and blocked the iOS upload).
- Skip Android release lint (network dependency check hangs on the build
  host and adds no value for a Flutter app).

app/lib/providers/contacts_provider.dart

@@ -17,6 +17,15 @@ class ContactsNotifier extends AsyncNotifier<List<Contact>> {
     final storage = ref.read(storageProvider);
     final contacts = await future;
 
+    // Odkaz bez routingu (aid+da) = protistrana ho vytvořila dřív, než měla
+    // hotovou registraci. Přidat takový kontakt = časovaná bomba: první
+    // odeslání spadne na „nemá doručovací adresu". Odmítnout hned s
+    // jasnou hláškou. (Nullable routing má smysl jen na interních příjmových
+    // cestách — roster/_findOrCreateContact —, ne při ručním importu.)
+    if (identity.accountId == null || identity.deliveryAddress == null) {
+      throw const ContactLinkIncompleteError();
+    }
+
     // Kontrola duplicity
     if (contacts.any((c) => c.publicIdentity.id == identity.id)) {
       throw const ContactAlreadyExistsError();