[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_login.cpp

@@ -1,8 +1,11 @@
 #include "intent_login.h"
 
 #include "../../client/settings/cache_settings.h"
+#include "../widgets/dialogs/dlg_login_prompt.h"
 #include "libcockatrice/settings/servers_settings.h"
 
+#include <QDialog>
+
 IntentGetLoginCredentials::IntentGetLoginCredentials(ContextConnectToServer *_context) : Intent(), context(_context)
 {
 }
@@ -29,5 +32,27 @@ void IntentGetLoginCredentials::onPreconditionSatisfied()
 
 void IntentGetLoginCredentials::onPreconditionNotSatisfied()
 {
-    emitFailed(tr("No saved credentials for this server"));
+    // No credentials saved for the target server: ask the user for them. They
+    // opt into saving them so later links to the same server connect directly.
+    const QString serverText = context->hostname + ":" + context->port;
+    DlgLoginPrompt dialog(serverText);
+    // ApplicationModal: the dialog has no parent (the intent is not a widget),
+    // so WindowModal would not actually block any other window.
+    dialog.setWindowModality(Qt::ApplicationModal);
+
+    if (dialog.exec() != QDialog::Accepted) {
+        emitCancelled();
+        return;
+    }
+
+    context->username = dialog.username();
+    context->password = dialog.password();
+
+    if (dialog.savePassword() && !context->username.isEmpty()) {
+        ServersSettings &servers = SettingsCache::instance().servers();
+        servers.addNewServer(context->hostname, context->hostname, context->port, context->username, context->password,
+                             true);
+    }
+
+    emitFinished();
 }