fix: add keyboard focus indicator for sliders

[mhduiy]

修复内容

修复 PMS BUG-341415：dock 快捷面板滑块缺少键盘焦点指示器。

变更说明

在 SliderProxyStyle::drawComplexControl 方法中新增键盘焦点指示器绘制逻辑：

• 当滑块获得键盘焦点（QStyle::State_HasFocus）时，使用 DPalette::Highlight 颜色在 handle 周围绘制圆角焦点边框
• 对 RoundHandler 样式，焦点边框基于重新计算的正方形 handle 区域绘制，与 drawRoundSlider 实际绘制的圆形滑块完全对齐
• Normal 样式不受影响

关联信息

• PMS Bug: https://pms.uniontech.com/bug-view-341415.html
• Multica Issue: DDE-304

Summary by Sourcery

Add visible keyboard focus feedback for dock panel sliders.

Bug Fixes:

• Add a keyboard focus indicator around focused dock sliders to resolve the missing focus feedback issue.

Enhancements:

• Align the focus indicator with round slider handles while leaving normal slider rendering unchanged.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

The slider proxy style now renders a palette-highlight rounded focus ring around focused slider handles, with geometry adjusted for round handles to align with their actual circular rendering while preserving existing normal-slider behavior.

Flow diagram for slider keyboard focus indicator rendering

flowchart TD
    A["SliderProxyStyle::drawComplexControl"] --> B{State_HasFocus}
    B -->|No| C["drawNormalSlider or drawRoundSlider"]
    B -->|Yes| D["Get DPalette::Highlight"]
    D --> E{RoundHandler}
    E -->|Yes| F["Recalculate square handle geometry"]
    E -->|No| G["Use rectHandle geometry"]
    F --> H["Expand geometry by margin 3"]
    G --> H
    H --> I["Draw rounded focus border"]
    I --> J["Restore painter"]
    C --> J

Loading

File-Level Changes

Change	Details	Files
Add a keyboard-focus indicator around the slider handle when the control has focus.	Detect QStyle::State_HasFocus in the complex-control drawing path. Use the palette highlight color and a two-pixel pen to draw an unfilled rounded focus border with a three-pixel margin. Recompute the focused handle bounds for RoundHandler so the border aligns with the rendered circular handle. Leave the normal slider rendering path unchanged.	plugins/dde-dock/common/slidercontainer.cpp

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[mhduiy]

修改不合理，dde-tray-loader 是正确的样式，问题出在dtk，应该在DTK中修复