feat(ui): style app menus and extract glossary dialog

- Add AppMenu and AppMenuItem so menu labels, mnemonics and shortcuts render consistently under org.kde.union
- Move the translation glossary into GlossaryDialog with add, remove and clear-all actions
- Regroup the translation preset and instructions settings layout

src/qml/PlaylistItem.qml

@@ -113,15 +113,15 @@ Item {
         }
     }
 
-    Menu {
+    AppMenu {
         id: contextMenu
 
-        MenuItem {
+        AppMenuItem {
             text: KI18n.i18nc("@action:inmenu", "Play")
             icon.name: "media-playback-start"
             onTriggered: root.playlist.play(root.index)
         }
-        MenuItem {
+        AppMenuItem {
             text: KI18n.i18nc("@action:inmenu", "Open Containing Folder")
             icon.name: "folder-open"
             enabled: root.url.toString().startsWith("file://")
@@ -131,19 +131,19 @@ Item {
             }
         }
         MenuSeparator {}
-        MenuItem {
+        AppMenuItem {
             text: KI18n.i18nc("@action:inmenu", "Move Up")
             icon.name: "go-up"
             enabled: root.index > 0
             onTriggered: root.playlist.move(root.index, root.index - 1)
         }
-        MenuItem {
+        AppMenuItem {
             text: KI18n.i18nc("@action:inmenu", "Move Down")
             icon.name: "go-down"
             enabled: root.index < root.playlist.count - 1
             onTriggered: root.playlist.move(root.index, root.index + 1)
         }
-        MenuItem {
+        AppMenuItem {
             text: KI18n.i18nc("@action:inmenu", "Remove from Playlist")
             icon.name: "list-remove"
             onTriggered: root.playlist.remove(root.index)