feat(media): add toggle for album art accent colors (#2831) (#2832)

* fix(media): use system colours in player instead of album cover accent

Closes #2831

Removes ColorQuantizer-based album art accent extraction from
MediaAccentService. All accent properties now return Theme.primary
and Theme.onPrimary directly, so the Dank Dash player always
matches the system colour scheme.

Blame: ee6f7b47 (introduced MediaAccentService & ColorQuantizer)
       d799175c (tweaked seekbar accent colours)
       a62ae336 (further integrated accent into player/album art)
       c44ffae7 (monochrome art edge case fixes)

* feat(media): add toggle for album art accent colours (#2831)

Adds mediaUseAlbumArtAccent setting (default: off) to Settings.
When enabled, MediaAccentService extracts accent from album art
via ColorQuantizer. When disabled, uses Theme.primary.
Toggle is in Settings > Media Player.

* fix: use american english spelling (colour -> color)

Port 1.5

quickshell/Modules/Settings/MediaPlayerTab.qml

@@ -65,6 +65,13 @@ Item {
                     onToggled: checked => SettingsData.set("mediaAdaptiveWidthEnabled", checked)
                 }
 
+                SettingsToggleRow {
+                    text: I18n.tr("Use album art accent")
+                    description: I18n.tr("Use colors extracted from album art instead of system theme colors")
+                    checked: SettingsData.mediaUseAlbumArtAccent
+                    onToggled: checked => SettingsData.set("mediaUseAlbumArtAccent", checked)
+                }
+
                 SettingsDropdownRow {
                     property var scrollOptsInternal: ["volume", "song", "nothing"]
                     property var scrollOptsDisplay: [I18n.tr("Change Volume", "media scroll wheel option"), I18n.tr("Change Song", "media scroll wheel option"), I18n.tr("Nothing", "media scroll wheel option")]