Avalonia Migration Refactor

[taooceros]

Summary

Migration to Avalonia, based on dev, with unrelated fixes split out.

could potentially resolves #894.

Build/artifact wiring

• Flow.Launcher.sln adds Flow.Launcher.Avalonia so solution builds produce the Avalonia host.
• Flow.Launcher.Avalonia/Flow.Launcher.Avalonia.csproj writes host output to Output\Avalonia\$(Configuration).
• Built-in plugin .csproj files copy plugin outputs into Output\Avalonia\$(Configuration)\Plugins\... for Avalonia runtime loading.
• Scripts/post_build.ps1 packages Avalonia setup/portable artifacts separately under Output\Packages\Avalonia.
• .github/workflows/dotnet.yml uploads Avalonia Setup and Avalonia Portable Version artifacts.

What changed in the existing WPF/shared surface

These are the non-Flow.Launcher.Avalonia/ changes reviewers should expect:

• Flow.Launcher/Languages/en.xaml — shared localization keys used by Avalonia UI.
• Flow.Launcher.Infrastructure/Hotkey/GlobalHotkey.cs — exposes hotkey callback/key conversion needed by the Avalonia host.
• Flow.Launcher.Plugin/Interfaces/ISettingProvider.cs — adds CreateSettingPanelAvalonia() for native Avalonia plugin settings without exposing Avalonia types to WPF plugin reflection.
• Built-in plugin .csproj, Main.cs, and Views/Avalonia/* files — native Avalonia settings views and copy targets.
• Flow.Launcher.sln — includes the Avalonia project in normal solution builds.
• Scripts/post_build.ps1 and Scripts/flowlauncher-avalonia.nuspec — create Avalonia setup/portable artifacts without changing release deployment workflows.
• .github/workflows/dotnet.yml — uploads Avalonia CI artifacts only.

Existing WPF behavior intentionally left alone

• WPF host runtime behavior was not intentionally refactored.
• Existing WPF plugin settings remain the compatibility/fallback path.
• The JsonStorage temp-file truncation fix was split out to PR Fix JsonStorage temp file truncation #4558 and is no longer part of this PR.

Verification

CI artifact sizes from run 28725559998 before the JsonStorage split cleanup:

• Flow Installer: 101,089,952 bytes

• Portable Version: 204,621,638 bytes

• Avalonia Setup: 85,188,274 bytes

• Avalonia Portable Version: 172,204,291 bytes

• The original Flow Launcher installer works.

• The Avalonia installer works.

Review notes

Highest-risk areas:

• Flow.Launcher.Avalonia/AvaloniaPublicAPI.cs plugin API compatibility.
• Flow.Launcher.Avalonia/ViewModel/MainViewModel.cs query/result lifecycle and plugin async query behavior.
• Flow.Launcher.Avalonia/App.axaml.cs startup sequence, WPF resource compatibility shim, and plugin initialization.
• Build artifact paths: Avalonia must stay under Output\Avalonia\$(Configuration) so WPF package inputs under Output\Release remain close to dev.