feat(core,app,android,ios): finish adding a first share where it pays off

- A link with a password of its own, added without one, now fails as
  "This link has a password of its own" instead of the handshake's
  refusal. The link's public flags are only asked for after a refusal.
  The desktop form turns its password toggle on.
- After the first share is added, all three clients go to the library.
  While that share is being listed, the empty library says so instead of
  offering to add a share.
- The desktop library offers posters and synopses once there is a
  library to put them on. The offer says what is sent, links to
  Settings, never turns anything on, and "Not now" is remembered.

ios/ProtonStream/App/ProtonStreamApp.swift

@@ -181,7 +181,9 @@ struct RootView: View {
                 selectedTitleKey = title.key
             })
         case .shares:
-            SharesView(incomingLink: $incomingLink)
+            // The first share is the library: watch it fill rather than stay
+            // on a form that has done its job.
+            SharesView(incomingLink: $incomingLink, onFirstShareAdded: { select(.library) })
         case .downloads:
             DownloadsView()
         case .settings: