feat: support QStyleHints::colorScheme() to get light/dark theme

[BLumia]

Previously we don't support such feature, thus applications rely on this API to check system light/dark theme won't work. This make such API work.

Log:

验证方式：

import QtQuick

Rectangle {
    // Check if the current theme is Dark
    property bool isDarkMode: Application.styleHints.colorScheme === Qt.ColorScheme.Dark
    color: isDarkMode ? "dark" : "white"
    
    Component.onCompleted: {
        if (isDarkMode) {
            console.log("Current theme is DARK")
        } else {
            console.log("Current theme is LIGHT")
        }
    }
}

PMS: 369921

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[deepin-ci-robot]

deepin pr auto review

★ 总体评分：100分

■ 【总体评价】

代码实现了Qt6.5及以上版本的暗色与亮色主题方案获取功能，逻辑严谨且无安全风险
代码质量优秀，无任何安全漏洞及逻辑缺陷，保持满分

■ 【详细分析】

• 1.语法逻辑（完全正确）✓

函数 colorScheme() 在 qdeepintheme.cpp 中实现逻辑清晰，正确处理了 helper 为空的边界情况，switch 语句覆盖了所有枚举分支并包含 default 返回值。条件编译宏使用正确。
潜在问题：无
建议：无

• 2.代码质量（优秀）✓

代码符合 Qt 编码规范，命名清晰，条件编译保证了版本兼容性，结构简洁。
潜在问题：无
建议：无

• 3.代码性能（高效）✓

仅通过单例获取指针并进行简单的枚举判断，无额外开销。
建议：无

• 4.代码安全（存在0个安全漏洞）✓

漏洞对比统计：新增漏洞 0 个，减少漏洞 0 个，持平 0 个
代码仅读取应用内部主题状态，无外部输入交互，不存在攻击面。

• 建议：无需修复

■ 【改进建议代码示例】

+Qt::ColorScheme QDeepinTheme::colorScheme() const
+{
+    auto *helper = DGuiApplicationHelper::instance();
+    if (!helper)
+        return QGenericUnixTheme::colorScheme();
+
+    switch (helper->themeType()) {
+    case DGuiApplicationHelper::DarkType:
+        return Qt::ColorScheme::Dark;
+    case DGuiApplicationHelper::LightType:
+        return Qt::ColorScheme::Light;
+    default:
+        return Qt::ColorScheme::Unknown;
+    }
+}

[deepin-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: 18202781743, BLumia

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