[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.cpp

@@ -7,6 +7,7 @@
 #include "flow_widget.h"
 
 #include <QHBoxLayout>
+#include <QKeyEvent>
 #include <QResizeEvent>
 #include <QScrollArea>
 #include <QSizePolicy>
@@ -80,13 +81,35 @@ FlowWidget::FlowWidget(QWidget *parent,
 /**
  * @brief Adds a widget to the flow layout within the FlowWidget.
  *
+ * Plain widgets are not filtered for arrow keys: intercepting them would steal
+ * Up/Down/Left/Right from controls that use them (combo boxes, spin boxes
+ * etc.). Widgets that want keyboard navigation between flow items must be
+ * added via addNavigableWidget instead.
+ *
  * @param widget_to_add The widget to add to the flow layout.
  */
-void FlowWidget::addWidget(QWidget *widget_to_add) const
+void FlowWidget::addWidget(QWidget *widget_to_add)
 {
     flowLayout->addWidget(widget_to_add);
 }
 
+/**
+ * @brief Adds a widget and routes its arrow keys to FlowWidget focus navigation.
+ *
+ * The widget is filtered for arrow-key events so keyboard navigation between
+ * the flow items keeps working even when the flow sits inside a QScrollArea,
+ * which swallows arrow keys before they can reach FlowWidget::keyPressEvent.
+ * Only widgets added through this method are affected; anything that needs its
+ * own arrow keys should use plain addWidget.
+ *
+ * @param widget_to_add The widget to add to the flow layout.
+ */
+void FlowWidget::addNavigableWidget(QWidget *widget_to_add)
+{
+    widget_to_add->installEventFilter(this);
+    flowLayout->addWidget(widget_to_add);
+}
+
 void FlowWidget::insertWidgetAtIndex(QWidget *toInsert, int index)
 {
     flowLayout->insertWidgetAtIndex(toInsert, index);
@@ -177,6 +200,66 @@ QLayoutItem *FlowWidget::itemAt(int index) const
     return flowLayout->itemAt(index);
 }
 
+void FlowWidget::keyPressEvent(QKeyEvent *event)
+{
+    if (moveFocus(event)) {
+        event->accept();
+        return;
+    }
+    QWidget::keyPressEvent(event);
+}
+
+bool FlowWidget::eventFilter(QObject *watched, QEvent *event)
+{
+    if (event->type() == QEvent::KeyPress && moveFocus(static_cast<QKeyEvent *>(event))) {
+        return true;
+    }
+    return QWidget::eventFilter(watched, event);
+}
+
+bool FlowWidget::moveFocus(QKeyEvent *event)
+{
+    // Keyboard navigation between the flow items: arrow keys move focus just
+    // like clicking the sibling tiles would. Only items that can take keyboard
+    // focus (e.g. the deck-preview tiles in shared-deck links) are visited.
+    const bool moveForward = event->key() == Qt::Key_Right || event->key() == Qt::Key_Down;
+    const bool moveBackward = event->key() == Qt::Key_Left || event->key() == Qt::Key_Up;
+    if (!moveForward && !moveBackward) {
+        return false;
+    }
+
+    QList<QWidget *> focusableItems;
+    for (int i = 0; i < flowLayout->count(); ++i) {
+        QWidget *item = flowLayout->itemAt(i)->widget();
+        if (item != nullptr && (item->focusPolicy() & Qt::TabFocus)) {
+            focusableItems.append(item);
+        }
+    }
+
+    if (focusableItems.isEmpty()) {
+        return false;
+    }
+
+    int currentIndex = -1;
+    for (int i = 0; i < focusableItems.size(); ++i) {
+        if (focusableItems.at(i)->hasFocus()) {
+            currentIndex = i;
+            break;
+        }
+    }
+
+    const int delta = moveForward ? 1 : -1;
+    int nextIndex;
+    if (currentIndex < 0) {
+        nextIndex = moveForward ? 0 : focusableItems.size() - 1;
+    } else {
+        nextIndex = (currentIndex + delta + focusableItems.size()) % focusableItems.size();
+    }
+    focusableItems.value(nextIndex)->setFocus();
+    event->accept();
+    return true;
+}
+
 int FlowWidget::count() const
 {
     return flowLayout->count();