[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/dialogs/dlg_login_prompt.h

@@ -0,0 +1,40 @@
+/**
+ * @file dlg_login_prompt.h
+ * @ingroup ConnectionDialogs
+ */
+//! \todo Document this file.
+
+#ifndef DLG_LOGIN_PROMPT_H
+#define DLG_LOGIN_PROMPT_H
+
+#include <QDialog>
+
+class QCheckBox;
+class QLineEdit;
+
+/**
+ * @brief Small sign-in dialog used when a cockatrice:// link needs credentials
+ * that are not saved for the target server.
+ *
+ * The entered name and password are handed to the intent chain; when the user
+ * opts to save them, they are stored in the server settings so that later links
+ * to the same server connect seamlessly.
+ */
+class DlgLoginPrompt : public QDialog
+{
+    Q_OBJECT
+
+public:
+    explicit DlgLoginPrompt(const QString &serverText, QWidget *parent = nullptr);
+
+    [[nodiscard]] QString username() const;
+    [[nodiscard]] QString password() const;
+    [[nodiscard]] bool savePassword() const;
+
+private:
+    QLineEdit *usernameEdit;
+    QLineEdit *passwordEdit;
+    QCheckBox *savePasswordCheckBox;
+};
+
+#endif // DLG_LOGIN_PROMPT_H