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/RecentFilesMenu.qml

@@ -8,7 +8,7 @@ import QtQuick
 import QtQuick.Controls
 import org.kde.ki18n
 
-Menu {
+AppMenu {
     id: root
 
     required property Actions actions
@@ -18,7 +18,7 @@ Menu {
 
     Instantiator {
         model: RecentFilesModel
-        delegate: MenuItem {
+        delegate: AppMenuItem {
             required property url url
             required property string name
             required property string path
@@ -35,7 +35,7 @@ Menu {
 
     MenuSeparator {}
 
-    MenuItem {
+    AppMenuItem {
         text: KI18n.i18nc("@action:inmenu", "Clear List")
         icon.name: "edit-clear-history"
         onTriggered: RecentFilesModel.clear()