Fix MPRIS player duplication during internet radio (#1048) (#1069)

* fix(mpris): disable WebKit media session so radio doesn't duplicate the player

Internet radio plays through an HTML <audio> element, for which WebKitGTK
auto-registers its own MPRIS player (org.webkit.*) alongside the app's
souvlaki one. On Linux desktops that list every player, now-playing then
showed twice during radio (issue #1048: one "psysonic", one "Psysonic").

Disable the WebKit media session at main-window setup (enable-media-session,
set by GObject property name since the pinned binding has no typed setter,
guarded by find_property) so souvlaki stays the single now-playing source;
radio metadata still reaches it via mpris_set_metadata. The navigator.media
Session push in useRadioMprisSync is kept as a fallback in case a WebKitGTK
version still registers the player, so issue #816 cannot regress.

* docs(changelog): MPRIS radio duplication fix (PR #1069)

CHANGELOG.md

@@ -191,6 +191,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Fixed
 
+### Internet radio — no more duplicate now-playing on Linux
+
+**By [@Psychotoxical](https://github.com/Psychotoxical), reported by agriffit79, PR [#1069](https://github.com/Psychotoxical/psysonic/pull/1069)**
+
+* On Linux, playing an internet radio station showed the track twice in the desktop "now playing" overlay — once from the app's own media controls and once from a second player the web engine registered for the stream. The extra player is now suppressed, so radio shows a single entry like regular tracks.
+
 ### Fullscreen player — title cleanup
 
 **By [@Psychotoxical](https://github.com/Psychotoxical), PR [#1068](https://github.com/Psychotoxical/psysonic/pull/1068)**