Add font fallback settings

[Copilot]

Users had no way to specify fallback fonts for characters not covered by their primary fonts (e.g., CJK glyphs). This adds a FontFallback preference that appends user-specified fonts to both the default and monospace font chains.

Changes

• ViewModels/Preferences.cs: Added FontFallback property; updated DefaultFontFamily and MonospaceFontFamily setters to include _fontFallback in SetFonts calls
• App.axaml.cs: SetFonts now accepts a fallbackFont parameter — appended to Fonts.Default and Fonts.Monospace. When only fallbackFont is set (no custom default font), Inter is preserved as primary: fonts:Inter#Inter,{fallbackFont}
• Views/Preferences.axaml: New "Font Fallback" text field in the Appearance tab, after Monospace Font
• en_US.axaml: Added Text.Preferences.Appearance.FontFallback key

Behavior

State	Fonts.Default	Fonts.Monospace
Only fallbackFont set	fonts:Inter#Inter,{fallback}	fonts:SourceGit#JetBrains Mono,{fallback}
defaultFont + fallbackFont	{default},{fallback}	fonts:SourceGit#JetBrains Mono,{default},{fallback}
All three set	{default},{fallback}	{mono},{default},{fallback}

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:

• av-build-tel-api-v1.avaloniaui.net
  • Triggering command: /usr/share/dotnet/dotnet dotnet exec --runtimeconfig /home/REDACTED/.nuget/packages/avalonia.buildservices/11.3.2/tools/netstandard2.0/runtimeconfig.json /home/REDACTED/.nuget/packages/avalonia.buildservices/11.3.2/tools/netstandard2.0/Avalonia.BuildServices.Collector.dll /home/REDACTED/work/sourcegit/sourcegit/src/Views/MergeMultiple.axaml /home/REDACTED/work/sourcegit/sourcegit/src/Views/FilterModeSwitchButton.axaml /home/REDACTED/work/sourcegit/sourcegit/src/Views/ChangeSubmoduleUrl.axaml /home/REDACTED/work/sourcegit/sourcegit/src/Views/PushTag.axaml /home/REDACTED/work/sourcegit/sourcegit/src/Views/CreateBranch.axaml /home/REDACTED/work/sourcegit/sourcegit/src/Views/DeleteBranch.axaml /home/REDACTED/work/sourcegit/sourcegit/src/Views/LauncherTabBar.axaml (dns block)
  • Triggering command: /usr/share/dotnet/dotnet dotnet exec --runtimeconfig /home/REDACTED/.nuget/packages/avalonia.buildservices/0.0.28/tools/netstandard2.0/runtimeconfig.json /home/REDACTED/.nuget/packages/avalonia.buildservices/0.0.28/tools/netstandard2.0/Avalonia.BuildServices.Collector.dll (dns block)
• nuget-feed-all.avaloniaui.net
  • Triggering command: /usr/bin/dotnet dotnet build src/SourceGit.csproj owner --uid-owner 0 -j ACCEPT (dns block)
  • Triggering command: /opt/hostedtoolcache/CodeQL/2.24.0/x64/codeql/csharp/tools/linux64/Semmle.Autobuild.CSharp /opt/hostedtoolcache/CodeQL/2.24.0/x64/codeql/csharp/tools/linux64/Semmle.Autobuild.CSharp /var/lib/dpkg/info/libnuma1:amd64.list /var/lib/dpkg/info/emacsen-common.list /var/lib/dpkg/info/mysql-server-8.0.list (dns block)
  • Triggering command: /usr/bin/dotnet dotnet restore --no-dependencies /home/REDACTED/work/sourcegit/sourcegit/SourceGit.slnx --packages /home/REDACTED/work/sourcegit/.codeql-scratch/dbs/csharp/working/packages /p:DisableImplicitNuGetFallbackFolder=true --verbosity normal /p:TargetFrameworkRootPath=/home/REDACTED/work/sourcegit/.codeql-scratch/dbs/csharp/working/emptyFakeDotnetRoot /p:NetCoreTargetingPackRoot=/home/REDACTED/work/sourcegit/.codeql-scratch/dbs/csharp/working/emptyFakeDotnetRoot /p:AllowMissingPrunePackageData=true (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.