feat(sounds): make muting sounds during media playback configurable (#2652)

Commit e3dbaed started skipping all system sounds (notifications, volume,
power, login) whenever an MPRIS player is playing, with no way to opt out.
Users who rely on notification sounds while listening to music lost them
entirely.

Add a 'Mute During Playback' toggle (SettingsData.muteSoundsWhenMediaPlaying,
default true) so the current behaviour is preserved, but users can disable
it to restore audible sounds while media is playing. The media check is
wrapped in shouldMuteForMedia(), which gates on the new setting before
querying the active player.

Closes #2616

quickshell/Modules/Settings/SoundsTab.qml

@@ -131,6 +131,23 @@ Item {
                         checked: SettingsData.soundPluggedIn
                         onToggled: checked => SettingsData.set("soundPluggedIn", checked)
                     }
+
+                    Rectangle {
+                        width: parent.width
+                        height: 1
+                        color: Theme.outline
+                        opacity: 0.2
+                    }
+
+                    SettingsToggleRow {
+                        tab: "sounds"
+                        tags: ["sound", "media", "playback", "mute", "mpris", "music"]
+                        settingKey: "muteSoundsWhenMediaPlaying"
+                        text: I18n.tr("Mute During Playback")
+                        description: I18n.tr("Silence system sounds while media is playing")
+                        checked: SettingsData.muteSoundsWhenMediaPlaying
+                        onToggled: checked => SettingsData.set("muteSoundsWhenMediaPlaying", checked)
+                    }
                 }
             }