fix: expose dialog aliases so About and Manual+ open (1.0.8)

HeaderNavigation and StationCard access dialogs via app.aboutDialog etc.,
but Main.qml never exported those ids as property aliases after the QML
module refactor. Align AboutDialog anchoring with the other dialogs.

src/qml/Main.qml

@@ -34,6 +34,9 @@ ApplicationWindow {
     property string countrySearchText: ""
     property alias searchField: searchToolbar.searchField
     property alias stationList: stationPanel.stationList
+    property alias addDialog: addDialog
+    property alias editDialog: editDialog
+    property alias aboutDialog: aboutDialog
 
     function toast(message) {
         toastPopup.show(message)

src/qml/components/AboutDialog.qml

@@ -11,11 +11,11 @@ Dialog {
     id: root
 
     required property bool compactMode
-    required property string appVersion
-    required property string buildId
+    property string appVersion: Qt.application.version
+    property string buildId: "?"
 
     modal: true
-    anchors.centerIn: Overlay.overlay
+    anchors.centerIn: parent
     width: compactMode ? 360 : 520
     height: compactMode ? 560 : 680
     standardButtons: Dialog.Ok