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/Main.qml

@@ -318,39 +318,8 @@ ApplicationWindow {
         onAccepted: video.addSubtitleFile(selectedFile)
     }
 
-    Kirigami.Dialog {
+    GlossaryDialog {
         id: glossaryDialog
-        title: KI18n.i18nc("@title:window", "Translation Glossary")
-        standardButtons: Kirigami.Dialog.Save | Kirigami.Dialog.Cancel
-        width: Math.min(appWindow.width * 0.9, 650)
-        contentItem: ColumnLayout {
-            ListView {
-                id: glossaryList
-                Layout.fillWidth: true
-                Layout.fillHeight: true
-                Layout.preferredHeight: Kirigami.Units.gridUnit * 15
-                clip: true
-                model: ListModel { id: glossaryModel }
-                delegate: RowLayout {
-                    width: glossaryList.width
-                    TextField { text: source; Layout.fillWidth: true; onTextChanged: model.source = text }
-                    TextField { text: target; Layout.fillWidth: true; onTextChanged: model.target = text }
-                    ToolButton { icon.name: "edit-delete-remove"; onClicked: glossaryModel.remove(index) }
-                }
-            }
-            RowLayout {
-                Button { text: KI18n.i18nc("@action:button", "Add"); onClicked: glossaryModel.append({source: "", target: ""}) }
-                Button { text: KI18n.i18nc("@action:button", "Clear"); onClicked: glossaryModel.clear() }
-            }
-        }
-        onOpened: {
-            glossaryModel.clear()
-            for (const entry of translationService.glossaryEntries) glossaryModel.append(entry)
-        }
-        onAccepted: {
-            const entries = []
-            for (let i = 0; i < glossaryModel.count; ++i) entries.push(glossaryModel.get(i))
-            translationService.saveGlossary(entries)
-        }
+        translator: translationService
     }
 }