feat: register cockatrice:// and cockatrice-oracle:// protocol handlers

Adds OS-level URL-scheme handlers so users can click a link in a browser,
chat client, or third-party tool to launch Cockatrice straight into a
server / game / Oracle update.

Supported URL forms:
  cockatrice://joingame?hostname=H&port=P&roomid=R&gameid=G[&spectate=1]
  cockatrice-oracle://update[?spoilers=1]

Credentials passed via URL (username/password query params) are deliberately
ignored — URLs leak through shell history, browser history, EDR capture, etc.
If the target server requires auth and no saved credentials match, the Connect
dialog opens pre-filled with the URL's host/port so the user types their
password locally.

OS integration
- Linux: MimeType=x-scheme-handler/cockatrice (and -oracle) added to the
  .desktop files; Exec=cockatrice %u passes the URL through.
- Windows: NSIS installer writes HKCR\cockatrice and HKCR\cockatrice-oracle
  registry entries; uninstaller removes them.
- macOS: per-app Info.cockatrice.plist / Info.oracle.plist declare
  CFBundleURLTypes; a QFileOpenEvent filter is installed on QApplication
  before any nested event loop so cold-start URLs aren't lost.

New abstractions
- Intent (libcockatrice_utility/libcockatrice/utility/intent.h): abstract base
  for chained async actions.  Guarantees finished() fires at most once,
  execute() is idempotent, self-deletes via deleteLater, and
  startTimeoutSafetyNet() arms a configurable per-stage deadline.  Concrete
  intents (IntentConnectToServer, IntentLogin, IntentJoinServerRoom,
  IntentJoinServerGame) compose the joingame flow via UrlParser.
- SingleInstanceManager: async per-user local-socket primary/secondary
  handshake; URL forwarded from secondary to primary with QDataStream framing
  both ways.  shared_ptr-backed resolved flag survives every lambda capture.
- UrlSchemeEventFilter (new libcockatrice_utility_gui sibling library): QObject
  event filter that translates macOS QFileOpenEvent into a urlReceived(QString)
  signal.  Lives in its own Gui-bearing lib so libcockatrice_utility stays
  Core+Network only and doesn't drag Qt::Gui into servatrice.
- UrlUtils (header-only): pure URL parsing, fully unit-tested.

Wiring
- MainWindow::handleUrl(QString) — single entry point for any URL source.
- DlgConnect::prefillNewHost(host, port) — pre-fills new-host inputs.
- ServersSettings::findSavedCredsByHostPort — case-insensitive saved-creds
  lookup.
- TabSupervisor::requestJoinRoom + roomJoinedById / roomJoinFailedById signals,
  TabServer::roomAlreadyJoined for the short-circuit "already in this room"
  path — single source of truth for duplicate-join handling.

Tests
- 36 new unit tests across four single-purpose targets in tests/:
  - url_utils_test (22 tests) — scheme matching, port/room/game validation,
    spectator flag, credentials ignored, case-insensitivity.
  - url_scheme_event_filter_test (3 tests) — QFileOpenEvent capture.
  - intent_test (7 tests) — self-delete, abort propagation, parent-destruction-
    mid-flight, finish-once gate, execute() idempotence.
  - single_instance_manager_test (4 tests) — per-user socket naming, becoming-
    primary alone, forwarding to an existing primary, single-emission of
    roleResolved.

Build tooling (incidental)
- Dockerfile.format, docker-compose.format.yml, Makefile — a docker-based
  runner for format.sh that mirrors CI's desktop-lint step.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

oracle/src/main.cpp

@@ -10,6 +10,8 @@
 #include <QLibraryInfo>
 #include <QTimer>
 #include <QTranslator>
+#include <libcockatrice/utility/url_utils.h>
+#include <libcockatrice/utility_gui/url_scheme_event_filter.h>
 
 QTranslator *translator, *qtTranslator;
 ThemeManager *themeManager;
@@ -63,10 +65,26 @@ int main(int argc, char *argv[])
     QCommandLineOption backgroundOption("b", QCoreApplication::translate("main", "Run in no-confirm background mode"));
     parser.addOption(spoilersOnlyOption);
     parser.addOption(backgroundOption);
+    parser.addPositionalArgument(
+        "url", QCoreApplication::translate("main", "Optional cockatrice-oracle:// URL to handle"), "[url]");
     parser.process(app);
     isSpoilersOnly = parser.isSet(spoilersOnlyOption);
     isBackgrounded = parser.isSet(backgroundOption);
 
+    // Handle cockatrice-oracle:// URL passed via the OS URL scheme handler
+    const QString oracleUrl =
+        UrlUtils::findUrlArgument(parser.positionalArguments(), QStringLiteral("cockatrice-oracle://"));
+    if (!oracleUrl.isEmpty()) {
+        const auto action = UrlUtils::parseOracleUrl(oracleUrl);
+        if (action.isUpdate) {
+            isBackgrounded = true;
+            if (action.spoilersOnly)
+                isSpoilersOnly = true;
+        } else {
+            qDebug() << "Oracle: ignoring unknown cockatrice-oracle:// URL:" << oracleUrl;
+        }
+    }
+
 #ifdef Q_OS_MAC
     translationPath = qApp->applicationDirPath() + "/../Resources/translations";
 #elif defined(Q_OS_WIN)
@@ -88,6 +106,27 @@ int main(int argc, char *argv[])
     // set name of the app desktop file; used by wayland to load the window icon
     QGuiApplication::setDesktopFileName("oracle");
 
+#ifdef Q_OS_MAC
+    // On macOS the OS delivers a registered URL scheme via QFileOpenEvent,
+    // dispatched on the first event-loop spin.  Oracle has no nested event
+    // loop before app.exec(), so installing the filter here (after wizard
+    // construction but before app.exec()) is sufficient — the cold-start URL
+    // event sits in the queue until app.exec() dispatches it, by which point
+    // both the filter and wizard exist.
+    UrlSchemeEventFilter oracleFilter(QStringLiteral("cockatrice-oracle://"));
+    QObject::connect(&oracleFilter, &UrlSchemeEventFilter::urlReceived, &wizard, [&wizard](const QString &url) {
+        const auto action = UrlUtils::parseOracleUrl(url);
+        if (!action.isUpdate) {
+            qDebug() << "Oracle: ignoring unknown cockatrice-oracle:// URL:" << url;
+            return;
+        }
+        if (action.spoilersOnly)
+            isSpoilersOnly = true;
+        QTimer::singleShot(0, &wizard, [&wizard]() { wizard.runInBackground(); });
+    });
+    app.installEventFilter(&oracleFilter);
+#endif
+
     wizard.show();
 
     if (isBackgrounded) {