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/l10n/app_ru.arb

@@ -75,6 +75,8 @@
   "chatEdited": "изменено",
   "errorTrustRootChanged": "Trust root релея изменился! Соединение отклонено.",
   "errorRelayUnavailable": "Релей недоступен (sender certificate)",
+  "errorNotYetRegistered": "Šepot ещё подключается к релею — попробуйте отправить сообщение через пару секунд.",
+  "errorContactLinkIncomplete": "Ссылка неполная — собеседник создал её до подключения. Попросите у него новую ссылку sepot://.",
   "errorAttachmentTooLarge": "Вложение слишком большое (макс. {maxMb} МБ)",
   "errorGroupNeedsMember": "В группе должен быть хотя бы 1 участник",
   "errorGroupMaxMembers": "Максимальное число участников группы — {maxMembers}",
@@ -294,6 +296,8 @@
   "chatListArchive": "Архивировать",
   "qrShareTitle": "Мой Šepot ID",
   "qrIdentityNotFound": "Идентичность не найдена",
+  "qrShareConnectingTitle": "Подключение к релею…",
+  "qrShareConnectingBody": "Ваш QR-код и ссылка появятся, как только Šepot подключится в первый раз. Подождите пару секунд.",
   "commonCopiedToClipboard": "Скопировано в буфер обмена",
   "qrShareInviteMessage": "Добавьте меня в Šepot!\n\n{shareString}",
   "commonShare": "Поделиться",