[DeckShare] Open shared decks via links with a gated preview flow (#7244)

* [DeckShare] Open shared decks via links with a gated preview flow

- Serialized url-chain dispatcher in IntentUrlParser; queue-drained
  urlChainFinished(bool) drives the startup auto-connect fallback
- Open-shared-deck intent with sequential download state machine,
  15s per-item timeout, partial-success offer, livable Cancel via
  ApplicationModal dlg_login_prompt interactive fallback
- Preview dialog: download progress label, share vocab sweep,
  palette-highlight selection frame, Space/Enter keyboard toggle,
  NoFocus checkbox, double-click tile opens immediately
- Confirm-before-server-migration with one-shot restore to the
  previous server on failed/cancelled chains (statusChanged settle
  deferral), hostname-only identity comparisons
- Skip credential link when already connected; arrow-key navigation
  in FlowWidget; card glows use palette highlight
- Address code-review M1-M4 and UI/UX QA blockers 1-2

* [DeckShare] End the open-shared-deck files with a trailing newline

* [DeckShare] Forward a dependency's cancellation as the owner's own

* [DeckShare] Let intent chains opt into the link sign-in dialog

* [DeckShare] Track link-intent chains per-run so each can restore its own session

* [Settings] Match a server on the exact host and port when adding it

* [DeckShare] Confirm the share link's target server before opening a deck

* [DeckShare] Reformat the link sign-in intent constructor

* [DeckShare] Time the share-list round trip and backstop silently-destroyed intent chains

* [Client] Drain a single-instance payload before its handlers read the socket again

* [Client] Treat a busy single-instance primary as alive instead of stealing its socket

* [DeckShare] Keep arrow-key navigation between flow items inside a scroll area

* [Client] Skip the startup connection when a macOS URL launch owns the connection

* [Client] Redact share secrets from activation URL logs

* [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

---------

Co-authored-by: Lukas Brübach <Bruebach.Lukas@bdosecurity.de>

cockatrice/src/interface/window_main.h

@@ -80,6 +80,7 @@ public slots:
     void actCheckClientUpdates();
     void actConnect();
     void actExit();
+    void handleCockatriceLink(const QString &url);
 private slots:
     void updateTabMenu(const QList<QMenu *> &newMenuList);
     void statusChanged(ClientStatus _status);
@@ -97,7 +98,7 @@ private slots:
     void actOpenSettingsFolder();
     void actShow();
     void showWindowIfHidden();
-    void handleCockatriceLink(const QString &url);
+    void onUrlChainFinished(bool connected);
 
     void cardUpdateError(QProcess::ProcessError err);
     void cardUpdateFinished(int exitCode, QProcess::ExitStatus exitStatus);
@@ -126,6 +127,8 @@ private slots:
     void startupDestinationFailed(const QString &reason);
     [[nodiscard]] bool startupDestinationConnectsToServer() const;
 
+    void attemptStartupAutoConnect();
+
 private:
     static const QString appName;
     static const QStringList fileNameFilters;
@@ -164,6 +167,8 @@ private:
     LagMonitor lagMonitor;                        ///< watches the main thread for event loop stalls
     LatencyStatusWidget *latencyStatus = nullptr; ///< status bar widget with live round-trip stats and history graph
     bool bHasActivated, askedForDbUpdater;
+    bool skipStartupAutoConnect = false;
+    bool startupAutoConnectAttempted = false;
     QProcess *cardUpdateProcess;
     QByteArray cardUpdateOutputBuffer;
     DlgViewLog *logviewDialog;
@@ -177,6 +182,16 @@ public:
     {
         connectTo = QUrl(QString("cockatrice://%1").arg(url));
     }
+    // When set, the window's own startup connection (--connect or auto-connect
+    // on first activation) is skipped. Used for activation launches: the intent
+    // chain triggered by a cockatrice:// URL owns the connection, and letting
+    // auto-connect race against it caused two connectToServer calls to tear
+    // each other down. onUrlChainFinished() clears this and retries the startup
+    // connection when the link's chain ended without connecting.
+    void setSkipStartupAutoConnect(bool skip)
+    {
+        skipStartupAutoConnect = skip;
+    }
     ~MainWindow() override;
 
     RemoteClient *getRemoteClient() const