Add mstsc embedding feasibility analysis based on existing COM/native-host architecture

[Copilot]

This issue asks whether the project’s current COM-based, WinForms-independent embedding approach (used for WebView1/WebView2) can be extended to mstsc. This PR adds a focused technical analysis of feasibility, implementation strategy, and key risks.

• What was added

  • New investigation document: docs/mstsc-feasibility.md

• Repository findings (project-specific)

  • Maps current embedding architecture relevant to mstsc:
    • adapter abstraction (IWebViewAdapter / WebViewAdapter)
    • native host integration (NativeWebViewControlHost)
    • Windows-side COM/HWND lifecycle patterns (WebView1/WebView2 paths)

• mstsc feasibility conclusion

  • Assesses Remote Desktop ActiveX (mstscax.dll) integration as feasible with medium-high complexity
  • Clarifies that Avalonia-side hosting patterns are reusable; primary difficulty is ActiveX host behavior, lifecycle, focus/input, and compatibility

• Implementation guidance captured

  • Recommends PoC-first scope:
    • create/embed control
    • connect/disconnect
    • resize/focus/dispose stability
  • Defines key engineering concerns:
    • STA/thread affinity
    • COM/event teardown ordering
    • security defaults (credentials, cert handling, redirection policy)
    • Windows/version dependency boundaries

# 研究：在 Avalonia.Controls.WebView 思路下内嵌 mstsc（Remote Desktop ActiveX）可行性
## 3. 可行性结论
**可行，但复杂度中到高，建议以 PoC 先行。**

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• learn.microsoft.com
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node /home/REDACTED/work/_temp/ghcca-node/node/bin/node --enable-source-maps /home/REDACTED/work/_temp/copilot-developer-action-main/dist/index.js (dns block)
• nuget-feed-all.avaloniaui.net
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  • Triggering command: /usr/bin/dotnet dotnet test tests/Avalonia.Controls.WebView.Tests/Avalonia.Controls.WebView.Tests.csproj -nologo (dns block)
• xpf-nuget-feed.avaloniaui.net
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If you need me to access, download, or install something from one of these locations, you can either:

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