[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/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>
@@ -28,7 +29,8 @@ public:
                Qt::ScrollBarPolicy horizontalPolicy,
                Qt::ScrollBarPolicy verticalPolicy);
 
-    void addWidget(QWidget *widget_to_add) const;
+    void addWidget(QWidget *widget_to_add);
+    void addNavigableWidget(QWidget *widget_to_add);
     void insertWidgetAtIndex(QWidget *toInsert, int index);
     void removeWidget(QWidget *widgetToRemove) const;
     void clearLayout();
@@ -43,9 +45,15 @@ public slots:
     void setSpacing(int hSpacing, int vSpacing);
 
 protected:
+    bool eventFilter(QObject *watched, QEvent *event) override;
     void resizeEvent(QResizeEvent *event) override;
+    void keyPressEvent(QKeyEvent *event) override;
 
 private:
+    /// @brief Moves keyboard focus to an adjacent flow item for an arrow-key event.
+    /// @return True when the event was an arrow key and was handled.
+    bool moveFocus(QKeyEvent *event);
+
     Qt::Orientation flowDirection;
     QHBoxLayout *mainLayout;
     FlowLayout *flowLayout;