feat(dialogs): make dialog button intent explicit per dialog

Each dialog now declares its own standard buttons rather than relying
on the base dialog's OK-only default, so the intent is clear and correct
at every call site.

Settings dialogs gain a Cancel button to expose a visible discard path;
previously the rollback was only reachable via Escape, with no button to
indicate that changes could be discarded. Informational dialogs use
Close, whose dismiss semantics fit a dialog that has nothing to accept.

With every dialog now specifying its buttons explicitly, the base
default is redundant and removed.

Author: trin94

qt/qml/io/github/mpvqc/mpvQC/Components/MpvqcDialog.qml

@@ -21,7 +21,6 @@ Dialog {
     dim: false
     z: 2
     closePolicy: Popup.CloseOnEscape
-    standardButtons: Dialog.Ok
 
     Binding {
         when: root.popupType === Popup.Window

qt/qml/io/github/mpvqc/mpvQC/Dialogs/MpvqcAboutDialog.qml

@@ -35,6 +35,7 @@ MpvqcDialog {
     readonly property int rowSpacing: 10
 
     contentHeight: Math.min(720, MpvqcWindowUtility.appHeight * 0.65)
+    standardButtons: Dialog.Close
 
     contentItem: ScrollView {
         readonly property bool isVerticalScollBarShown: contentHeight > root.contentHeight

qt/qml/io/github/mpvqc/mpvQC/Dialogs/MpvqcAppearanceDialog.qml

@@ -39,6 +39,7 @@ MpvqcDialog {
     contentHeight: MpvqcConstants.smallDialogContentHeight
 
     title: qsTranslate("AppearanceDialog", "Appearance")
+    standardButtons: Dialog.Ok | Dialog.Cancel
 
     component SelectionDelegate: ItemDelegate {
         id: delegateRoot

qt/qml/io/github/mpvqc/mpvQC/Dialogs/MpvqcBackupDialog.qml

@@ -24,6 +24,7 @@ MpvqcDialog {
     contentHeight: MpvqcConstants.smallDialogContentHeight
 
     title: qsTranslate("BackupDialog", "Backup Settings")
+    standardButtons: Dialog.Ok | Dialog.Cancel
 
     contentItem: ColumnLayout {
 

qt/qml/io/github/mpvqc/mpvQC/Dialogs/MpvqcExportSettingsDialog.qml

@@ -3,6 +3,7 @@
 // SPDX-License-Identifier: GPL-3.0-or-later
 
 import QtQuick
+import QtQuick.Controls.Material
 import QtQuick.Layouts
 
 import io.github.mpvqc.mpvQC.Components
@@ -18,6 +19,7 @@ MpvqcDialog {
     contentHeight: MpvqcConstants.smallDialogContentHeight
 
     title: qsTranslate("ExportSettingsDialog", "Export Settings")
+    standardButtons: Dialog.Ok | Dialog.Cancel
 
     contentItem: ColumnLayout {
         spacing: 10

qt/qml/io/github/mpvqc/mpvQC/Dialogs/MpvqcImportSettingsDialog.qml

@@ -19,6 +19,7 @@ MpvqcDialog {
     contentHeight: MpvqcConstants.smallDialogContentHeight
 
     title: qsTranslate("ImportSettingsDialog", "Import Settings")
+    standardButtons: Dialog.Ok | Dialog.Cancel
 
     contentItem: ColumnLayout {
         spacing: 10

qt/qml/io/github/mpvqc/mpvQC/Dialogs/MpvqcShortcutDialog.qml

@@ -21,6 +21,7 @@ MpvqcDialog {
 
     contentWidth: MpvqcConstants.mediumDialogContentWidth
     contentHeight: Math.min(720, MpvqcWindowUtility.appHeight * 0.65)
+    standardButtons: Dialog.Close
 
     contentItem: ColumnLayout {
         spacing: 0