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/TranslationSettings.qml

@@ -147,36 +147,35 @@ SettingsBasePage {
 
             Label {
                 text: KI18n.i18nc("@label:listbox", "Preset")
-                Layout.alignment: Qt.AlignRight | Qt.AlignTop
+                Layout.alignment: Qt.AlignRight | Qt.AlignVCenter
             }
 
-            ColumnLayout {
+            ComboBox {
+                id: presetCombo
                 Layout.fillWidth: true
-
-                ComboBox {
-                    id: presetCombo
-                    Layout.fillWidth: true
-                    model: root.translator.translationPresets
-                    textRole: "name"
-                    valueRole: "id"
-                    Component.onCompleted: currentIndex = Math.max(0, indexOfValue(QtPotatoSettings.translationPreset))
-                    onActivated: {
-                        QtPotatoSettings.translationPreset = currentValue
-                        QtPotatoSettings.save()
-                    }
+                model: root.translator.translationPresets
+                textRole: "name"
+                valueRole: "id"
+                Component.onCompleted: currentIndex = Math.max(0, indexOfValue(QtPotatoSettings.translationPreset))
+                onActivated: {
+                    QtPotatoSettings.translationPreset = currentValue
+                    QtPotatoSettings.save()
                 }
+            }
 
-                Label {
-                    text: presetCombo.currentIndex >= 0 ? presetCombo.model[presetCombo.currentIndex].guidance : ""
-                    wrapMode: Text.WordWrap
-                    opacity: 0.7
-                    Layout.fillWidth: true
-                }
+            Item { Layout.preferredWidth: 1 }
+
+            Label {
+                text: presetCombo.currentIndex >= 0 ? presetCombo.model[presetCombo.currentIndex].description : ""
+                wrapMode: Text.WordWrap
+                opacity: 0.7
+                font: Kirigami.Theme.smallFont
+                Layout.fillWidth: true
             }
 
             Label {
                 text: KI18n.i18nc("@label:textbox", "Additional instructions")
-                Layout.alignment: Qt.AlignRight | Qt.AlignTop
+                Layout.alignment: Qt.AlignRight | Qt.AlignBaseline
             }
 
             TextArea {
@@ -184,6 +183,7 @@ SettingsBasePage {
                 placeholderText: KI18n.i18nc("@info:placeholder", "e.g. Translate 'Young Master' as 'Thiếu gia'. Use 'ta/ngươi' between enemies.")
                 wrapMode: TextArea.Wrap
                 Layout.fillWidth: true
+                Layout.alignment: Qt.AlignBaseline
                 Layout.preferredHeight: Kirigami.Units.gridUnit * 4
                 // TextArea has no textEdited before Qt 6.9.
                 onTextChanged: QtPotatoSettings.customInstructions = text