[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/intents/intent_open_shared_deck.h

@@ -0,0 +1,59 @@
+#ifndef COCKATRICE_INTENT_OPEN_SHARED_DECK_H
+#define COCKATRICE_INTENT_OPEN_SHARED_DECK_H
+
+#include "contexts/context_open_deck.h"
+#include "intent.h"
+#include "remote_client.h"
+
+#include <QList>
+#include <QMap>
+#include <QScopedPointer>
+#include <memory>
+
+class TabSupervisor;
+struct LoadedDeck;
+class CardDatabaseQuerier;
+class DlgSharedDecksPreview;
+class QTimer;
+
+class IntentOpenSharedDeck : public Intent
+{
+    Q_OBJECT
+
+public:
+    IntentOpenSharedDeck(TabSupervisor *_tabSupervisor,
+                         RemoteClient *_remoteClient,
+                         const CardDatabaseQuerier *_querier,
+                         std::unique_ptr<ContextOpenDeck> _context);
+
+protected:
+    bool checkPrecondition() const override;
+    void onPreconditionSatisfied() override;
+    void onPreconditionNotSatisfied() override;
+
+private slots:
+    void listShareFinished(const Response &response, const CommandContainer &commandContainer);
+    void downloadShareFinished(const Response &response, const CommandContainer &commandContainer);
+    void onDownloadTimeout();
+
+private:
+    void startDownloads(const QList<int> &itemIds);
+    void downloadNextItem();
+    void onItemFailure(const QString &reason);
+    void finishAll();
+
+    TabSupervisor *tabSupervisor;
+    RemoteClient *remoteClient;
+    const CardDatabaseQuerier *querier;
+    QScopedPointer<ContextOpenDeck> context;
+    DlgSharedDecksPreview *previewDialog = nullptr;
+    QTimer *downloadTimer;
+    QMap<int, QString> itemNames;
+    QList<int> pendingItemIds;
+    QList<LoadedDeck> loadedDecks;
+    int currentItemId = 0;
+    int totalItems = 0;
+    int completedItems = 0;
+};
+
+#endif // COCKATRICE_INTENT_OPEN_SHARED_DECK_H