fix: add keyboard navigation for search dropdown

1. Root cause: SearchResultDialog.qml had no keyboard navigation;
   SearchEdit only handled Return key, arrow keys were consumed by
   TextField default cursor movement
2. Fix: add selectedIndex tracking, moveSelection/activateSelection
   methods and highlight in SearchResultDialog; add Keys.onDownPressed
   /onUpPressed and extend onReturnPressed in WindowTitlebar SearchEdit
3. Impact: users can now navigate search results with arrow keys and
   confirm with Enter; mouse interaction unchanged

Log: Search results now support keyboard navigation with arrow keys

Influence:
1. Test arrow key navigation in search result dropdown
2. Test Enter key to activate selected search result
3. Verify mouse hover and click still work as before

fix: 搜索结果下拉列表添加键盘导航

1. 根因：SearchResultDialog.qml 无键盘导航机制，SearchEdit 仅处理
   回车键，方向键被 TextField 默认光标移动行为消费
2. 方案：在 SearchResultDialog 添加 selectedIndex 追踪、
   moveSelection/activateSelection 方法和高亮显示；在 WindowTitlebar
   的 SearchEdit 添加方向键处理并扩展回车键逻辑
3. 影响：用户可通过方向键导航搜索结果并回车确认，鼠标交互不受影响

Log: 搜索结果支持方向键导航和回车选择

Influence:
1. 测试搜索结果下拉列表中方向键导航
2. 测试回车键激活选中的搜索结果
3. 验证鼠标悬停和点击功能无回归

PMS: BUG-375953

src/music-player/dialogs/SearchResultDialog.qml

@@ -12,11 +12,48 @@ Popup {
     property string pattern: ""
 
     property int itemHeight: 40
+    property int selectedIndex: -1
+    property int resultCount: (songList == null ? 0 : songList.length) + artistModel.count + albumModel.count
 
     signal searchItemTriggered(string value, int type)
 
     id: searchResultRect
     width: 360
+
+    // Moves the keyboard selection by offset, wrapping around available results.
+    function moveSelection(offset) {
+        if (resultCount <= 0)
+            return
+
+        if (selectedIndex < 0) {
+            selectedIndex = offset > 0 ? 0 : resultCount - 1
+            return
+        }
+
+        selectedIndex = (selectedIndex + offset + resultCount) % resultCount
+    }
+
+    // Activates the currently selected result and returns whether activation succeeded.
+    function activateSelection() {
+        if (selectedIndex < 0 || selectedIndex >= resultCount)
+            return false
+
+        var songCount = songList == null ? 0 : songList.length
+        if (selectedIndex < songCount) {
+            searchItemTriggered(songList[selectedIndex], 0)
+            return true
+        }
+
+        var artistIndex = selectedIndex - songCount
+        if (artistIndex < artistModel.count) {
+            searchItemTriggered(artistModel.get(artistIndex).name, 1)
+            return true
+        }
+
+        searchItemTriggered(albumModel.get(artistIndex - artistModel.count).name, 2)
+        return true
+    }
+
     height: (songList == null ? 0 : songList.length + artistModel.count + albumModel.count) * itemHeight + 110
     leftPadding: 8
     rightPadding: 8
@@ -66,10 +103,17 @@ Popup {
         id: resultItemTextDelegate
         Rectangle {
             id: itemRect
+            property int resultIndex: index
             width: parent.width
             height: itemHeight
             radius: 6
             color: "#00000000"
+            Rectangle {
+                anchors.fill: parent
+                radius: parent.radius
+                color: palette.highlight
+                visible: searchResultRect.selectedIndex === itemRect.resultIndex
+            }
             Row {
                 width: parent.width
                 anchors.verticalCenter: parent.verticalCenter
@@ -104,10 +148,20 @@ Popup {
         id: resultItemImgDelegate
         Rectangle {
             id: itemRect
+            property int resultIndex: (model.type === "album"
+                                       ? (searchResultRect.songList == null ? 0 : searchResultRect.songList.length)
+                                         + searchResultRect.artistModel.count
+                                       : (searchResultRect.songList == null ? 0 : searchResultRect.songList.length)) + index
             width: parent.width
             height: itemHeight
             radius: 6
             color: "#00000000"
+            Rectangle {
+                anchors.fill: parent
+                radius: parent.radius
+                color: palette.highlight
+                visible: searchResultRect.selectedIndex === itemRect.resultIndex
+            }
             Row {
                 width: parent.width
                 anchors.verticalCenter: parent.verticalCenter

src/music-player/mainwindow/WindowTitlebar.qml

@@ -272,12 +272,29 @@ TitleBar {
                 Layout.alignment: Qt.AlignCenter
                 placeholder: qsTr("Search")
                 enabled: Presenter.isExistMeta()
+                Keys.onDownPressed: function(event) {
+                    var searchResDlg = searchResultLoader.item
+                    if (!searchResDlg || !searchResDlg.visible)
+                        return
+                    searchResDlg.moveSelection(1)
+                    event.accepted = true
+                }
+                Keys.onUpPressed: function(event) {
+                    var searchResDlg = searchResultLoader.item
+                    if (!searchResDlg || !searchResDlg.visible)
+                        return
+                    searchResDlg.moveSelection(-1)
+                    event.accepted = true
+                }
                 Keys.onReturnPressed: {
                     //console.log("SearchEdit: Keys.onEnterPressed....")
                     var searchResDlg = searchResultLoader.item
                     if (text.length <= 0 || !searchResDlg || searchResDlg.songList == null)
                         return
 
+                    if (searchResDlg.visible && searchResDlg.activateSelection())
+                        return
+
                     var type = -1
                     if (searchResDlg.songList.length > 0)
                         type = 0
@@ -372,6 +389,7 @@ TitleBar {
         }
 
         var searchResDlg = searchResultLoader.item
+        searchResDlg.selectedIndex = -1
         searchResDlg.songList = []
         searchResDlg.artistModel.clear()
         searchResDlg.albumModel.clear()