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/android/app/build.gradle.kts

@@ -42,6 +42,14 @@ android {
         jvmTarget = JavaVersion.VERSION_17.toString()
     }
 
+    // Lint na release buildu vynechán: jeho síťové kontroly (novější verze
+    // závislostí) na omezené build síti visí donekonečna a pro Flutter appku
+    // nemají přínos. Analýzu Dartu dělá `flutter analyze`, Kotlin je minimální.
+    lint {
+        checkReleaseBuilds = false
+        abortOnError = false
+    }
+
     defaultConfig {
         applicationId = "cz.sepot.sepot"
         // libsignal binárky vyžadují Android 7.0+ (API 24)