fix(qrc): correct QML resource paths for AUR and release builds

The QML refactor in 1.0.4 used prefix /qml with file paths like
qml/Main.qml, embedding resources at qrc:/qml/qml/Main.qml while
main.cpp loads qrc:/qml/Main.qml. Use prefix / so paths match.

Also derive the displayed app version from CMake PROJECT_VERSION and
add a qrc_resources_test to prevent this regression in CI.

tests/qrc_resources_test.cpp

@@ -0,0 +1,30 @@
+// Copyright (c) 2026 Sebastian Palencsar
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#include <QFile>
+#include <QtTest>
+
+class QrcResourcesTest : public QObject
+{
+    Q_OBJECT
+
+private slots:
+    void mainQmlIsEmbedded();
+    void qmlModulesAreEmbedded();
+};
+
+void QrcResourcesTest::mainQmlIsEmbedded()
+{
+    QVERIFY2(QFile::exists(QStringLiteral(":/qml/Main.qml")),
+             "Main UI shell must be available at qrc:/qml/Main.qml");
+}
+
+void QrcResourcesTest::qmlModulesAreEmbedded()
+{
+    QVERIFY(QFile::exists(QStringLiteral(":/qml/theme/qmldir")));
+    QVERIFY(QFile::exists(QStringLiteral(":/qml/components/qmldir")));
+    QVERIFY(QFile::exists(QStringLiteral(":/assets/app/bearwave.png")));
+}
+
+QTEST_APPLESS_MAIN(QrcResourcesTest)
+#include "qrc_resources_test.moc"