新增官方QQ群入口及相关展示功能

[MayueCif]

在AppInfo中添加QQ群号和加入链接常量，About页面增加QQ群功能项及qq.svg图标，支持一键加入官方QQ群

[Copilot]

Pull request overview

This PR adds official QQ group integration to the MarketAssistant application's About page, enabling users to join the community group directly from the application. The change follows the existing pattern for feature items (changelog, website, feedback, license) and adds the necessary constants to centralize QQ group information.

Key Changes:

• Added QQ group number and join URL constants to AppInfo configuration
• Extended About page feature list with QQ group entry and join button
• Included QQ SVG icon for visual consistency

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/Applications/Settings/AppInfo.cs	Adds QQGroupNumber and QQGroupUrl constants to centralize QQ group information
src/ViewModels/AboutPageViewModel.cs	Adds QQ group feature item to the About page's feature list with icon, title, and join command
src/Assets/Images/qq.svg	Adds QQ icon SVG for the feature item display
src/ViewModels/HomePageViewModel.cs	Adds 'partial' keyword to align with codebase convention (unrelated to QQ feature)

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[Copilot]

The addition of the 'partial' keyword to HomePageViewModel appears to be unrelated to the QQ group feature described in this PR. While this change aligns with the codebase convention (all other ViewModels use 'partial' for MVVM Toolkit source generation), it should ideally be in a separate commit or PR focused on consistency improvements, or documented in the PR description as an additional fix.

Suggested change

	public partial class HomePageViewModel : ViewModelBase, IDisposable
	public class HomePageViewModel : ViewModelBase, IDisposable