refactor: source dialog sizes from MpvqcConstants

Dialog content width and height were spread across the base dialog
and several concrete dialogs as repeated magic numbers, leaving the
existing MpvqcConstants sizing values as the intended-but-unused
source of truth.

Point the dialogs at those shared constants so sizing lives in one
place and stays consistent, and so the previously orphaned
smallDialogContentWidth constant is actually used.

Author: trin94

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

@@ -7,14 +7,16 @@ pragma ComponentBehavior: Bound
 import QtQuick
 import QtQuick.Controls.Material
 
+import io.github.mpvqc.mpvQC.Utility
+
 Dialog {
     id: root
 
     readonly property bool isMirrored: Application.layoutDirection === Qt.RightToLeft
 
     popupType: Qt.platform.os === "windows" ? Popup.Window : Popup.Item
     anchors.centerIn: Overlay.overlay
-    contentWidth: 370
+    contentWidth: MpvqcConstants.smallDialogContentWidth
     modal: true
     dim: false
     z: 2

qt/qml/io/github/mpvqc/mpvQC/Dialogs/CommentTypes/MpvqcCommentTypesDialog.qml

@@ -10,14 +10,15 @@ import QtQuick.Layouts
 
 import io.github.mpvqc.mpvQC.Components
 import io.github.mpvqc.mpvQC.Python
+import io.github.mpvqc.mpvQC.Utility
 
 MpvqcDialog {
     id: root
     objectName: "commentTypesDialog"
 
     readonly property MpvqcCommentTypesDialogViewModel viewModel: MpvqcCommentTypesDialogViewModel {}
 
-    contentHeight: 450
+    contentHeight: MpvqcConstants.smallDialogContentHeight
 
     title: qsTranslate("CommentTypesDialog", "Comment Types")
     standardButtons: Dialog.Ok | Dialog.Cancel | Dialog.Reset

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

@@ -36,7 +36,7 @@ MpvqcDialog {
         readonly property int staggerInterval: 15
     }
 
-    contentHeight: 450
+    contentHeight: MpvqcConstants.smallDialogContentHeight
 
     title: qsTranslate("AppearanceDialog", "Appearance")
 

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

@@ -21,7 +21,7 @@ MpvqcDialog {
     readonly property int minBackupInterval: 15
     readonly property int maxBackupInterval: 5 * 60
 
-    contentHeight: 450
+    contentHeight: MpvqcConstants.smallDialogContentHeight
 
     title: qsTranslate("BackupDialog", "Backup Settings")
 

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

@@ -7,14 +7,15 @@ import QtQuick.Layouts
 
 import io.github.mpvqc.mpvQC.Components
 import io.github.mpvqc.mpvQC.Python
+import io.github.mpvqc.mpvQC.Utility
 
 MpvqcDialog {
     id: root
     objectName: "exportSettingsDialog"
 
     readonly property MpvqcExportSettingsDialogViewModel viewModel: MpvqcExportSettingsDialogViewModel {}
 
-    contentHeight: 450
+    contentHeight: MpvqcConstants.smallDialogContentHeight
 
     title: qsTranslate("ExportSettingsDialog", "Export Settings")
 

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

@@ -8,14 +8,15 @@ import QtQuick.Layouts
 
 import io.github.mpvqc.mpvQC.Components
 import io.github.mpvqc.mpvQC.Python
+import io.github.mpvqc.mpvQC.Utility
 
 MpvqcDialog {
     id: root
     objectName: "importSettingsDialog"
 
     readonly property MpvqcImportSettingsDialogViewModel viewModel: MpvqcImportSettingsDialogViewModel {}
 
-    contentHeight: 450
+    contentHeight: MpvqcConstants.smallDialogContentHeight
 
     title: qsTranslate("ImportSettingsDialog", "Import Settings")
 

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

@@ -19,7 +19,7 @@ MpvqcDialog {
 
     title: qsTranslate("ShortcutsDialog", "Keyboard Shortcuts")
 
-    contentWidth: 500
+    contentWidth: MpvqcConstants.mediumDialogContentWidth
     contentHeight: Math.min(720, MpvqcWindowUtility.appHeight * 0.65)
 
     contentItem: ColumnLayout {