[Client] Make the link-connection gates port-aware and keyboard-safe

Second-pass review notes for the shared-deck link flow (Cockatrice#7244):

- FlowWidget arrow-key navigation is opt-in via addNavigableWidget, so
  combo/spin controls on the analytics flows keep their own arrow keys
- isConnectedTo and the open-deck/join-game preconditions compare the
  configured server port alongside the host, so a same-host/different-port
  link cannot resolve its share token or game id on the wrong instance
- the link sign-in dialog reuses an existing server entry's saved name
  instead of renaming it to the raw hostname
- skipStartupAutoConnect is cleared once the launch chain connects, so a
  later mid-session declined link cannot fire the startup fallback
- the plain-launch path of SingleInstanceManager no longer blocks on the
  primary's ACK
- link- and server-supplied text is html-escaped in the confirm prompts and
  shared-deck preview so markup cannot spoof the shown messages

cockatrice/src/single_instance_manager.cpp

@@ -92,6 +92,14 @@ SingleInstanceManager::ForwardResult SingleInstanceManager::forwardToPrimary(con
     socket.flush();
     socket.waitForBytesWritten(1000);
 
+    // A plain launch has nothing for the primary to act on, so there is nothing
+    // to acknowledge. Waiting here would block the new instance for seconds if
+    // the primary is busy in a modal dialog, so only the activation path (which
+    // needs the ACK to avoid stealing a live primary's socket) waits below.
+    if (filesToSend.isEmpty()) {
+        return ForwardResult::Delivered;
+    }
+
     // Only report a successful hand-off once the primary has acknowledged that
     // it actually read the payload. A socket that connects but is still working
     // on an earlier payload is alive but busy, not dead: give it more room