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/pubspec.yaml

@@ -1,7 +1,7 @@
 name: sepot
 description: "Šepot — Soukromý messenger s E2E šifrováním"
 publish_to: 'none'
-version: 1.1.0+20
+version: 1.1.1+21
 
 environment:
   sdk: ^3.10.8
@@ -37,7 +37,10 @@ dependencies:
   pointycastle: ^3.9.1
   protobuf: ^6.0.0
   sqlite3: ^3.3.4
-  unifiedpush: ^6.2.0
+  # Pin pod 6.2.0: od 6.2.0 táhne unifiedpush_linux → webpush_encryption →
+  # webcrypto, jehož native framework na iOS chybí LC_ENCRYPTION_INFO (blokuje
+  # upload). Linux desktop neshipujeme, na Android/iOS je 6.1.x funkčně shodná.
+  unifiedpush: ">=6.1.0 <6.2.0"
   image: ^4.8.0
   mime: ^2.0.0
   image_picker: ^1.2.3