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/mprisadaptor.h

@@ -74,6 +74,8 @@ class MprisPlayerAdaptor : public QDBusAbstractAdaptor
 public:
     explicit MprisPlayerAdaptor(RadioBackend *backend);
 
+    void publishState();
+
     QString playbackStatus() const;
     double rate() const;
     void setRate(double value);