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/VideoMenu.qml

@@ -6,18 +6,18 @@ import QtQuick
 import QtQuick.Controls
 import org.kde.ki18n
 
-Menu {
+AppMenu {
     id: root
 
     required property Actions actions
 
     title: KI18n.i18nc("@title:menu", "&Video")
 
-    MenuItem { action: root.actions.toggleDeinterlacing }
-    MenuItem { action: root.actions.zoomIn }
-    MenuItem { action: root.actions.zoomOut }
-    MenuItem { action: root.actions.zoomReset }
-    MenuItem { action: root.actions.screenshot }
-    MenuItem { action: root.actions.rotateClockwise }
-    MenuItem { action: root.actions.rotateCounterClockwise }
+    AppMenuItem { action: root.actions.toggleDeinterlacing }
+    AppMenuItem { action: root.actions.zoomIn }
+    AppMenuItem { action: root.actions.zoomOut }
+    AppMenuItem { action: root.actions.zoomReset }
+    AppMenuItem { action: root.actions.screenshot }
+    AppMenuItem { action: root.actions.rotateClockwise }
+    AppMenuItem { action: root.actions.rotateCounterClockwise }
 }