[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

cockatrice/src/interface/widgets/general/layout_containers/flow_widget.h

@@ -11,6 +11,7 @@
 #include "../../../layouts/flow_layout.h"
 
 #include <QHBoxLayout>
+#include <QKeyEvent>
 #include <QLoggingCategory>
 #include <QScrollArea>
 #include <QWidget>
@@ -44,6 +45,7 @@ public slots:
 
 protected:
     void resizeEvent(QResizeEvent *event) override;
+    void keyPressEvent(QKeyEvent *event) override;
 
 private:
     Qt::Orientation flowDirection;