Fix playback, API races, tray, MPRIS, and search UX; add tests

- Correct history/resume next-previous context and list index resync after reload
- Abort stale RadioBrowser requests and suppress error banners when cache satisfies loads
- Reset local search filter on page changes and debounce compact-mode API search
- Move system tray to C++ (QSystemTrayIcon) for reliable Wayland context menus
- Harden MPRIS registration and metadata updates for Plasma media widgets
- Add playback and API race unit tests
- Drop unused KF6 Kirigami, I18n, and CoreAddons build dependencies
- Update packaging docs, CI, and PKGBUILD to match Qt-only requirements

src/radiobrowser.h

@@ -38,9 +38,13 @@ private slots:
 
 private:
     QNetworkAccessManager *m_networkManager = nullptr;
+    QNetworkReply *m_activeReply = nullptr;
     QString m_baseUrl = "https://all.api.radio-browser.info/json";
+    int m_requestGeneration = 0;
 
     void makeRequest(const QString &endpoint);
+    void emitCachedResponse(const QString &endpoint, const QString &cachePath, int requestGeneration);
+    bool isCountriesEndpoint(const QString &endpoint) const;
     QList<RadioStation*> parseJsonResponse(const QByteArray &jsonData);
     QVariantList parseCountriesJson(const QByteArray &jsonData);
 };