Feature/epona branch instances

[Caeldeth]

Description

Adds the minimal server-side support needed for Epona's branch-aware server instance management (multi-target expansion plan, Stage 3) and embedded-console mode (Stage 3.0 follow-up). Two small, independent changes: (1) a conditional Hybrasyl.Xml reference in Hybrasyl.csproj that lets Epona swap the NuGet package for a local ProjectReference via a gitignored Directory.Build.props, and (2) a Console.IsInputRedirected guard around the fatal-exit Console.ReadKey() in Game.cs so the server exits cleanly when launched with piped stdio instead of throwing InvalidOperationException. No behavior change for standalone terminal runs, CI, or developers not using Epona. Design docs added under docs/.

Related PRs

branch	PR

Checklist

• Tested and working locally
• Reviewed
• Tested and working on dev server
• Deployed to staging

How to QA

1. Default NuGet path (regression check): With no Directory.Build.props in the repo root, run dotnet build hybrasyl/Hybrasyl.csproj. Confirm it restores and builds against Hybrasyl.Xml 0.9.4.11 from NuGet exactly as before.
2. Local XML project reference: Create Directory.Build.props in the repo root with:

   <Project>
     <PropertyGroup>
       <UseLocalXml>true</UseLocalXml>
       <LocalXmlProjectPath>E:\Dark Ages Dev\Repos\xml\src\Hybrasyl.Xml.csproj</LocalXmlProjectPath>
     </PropertyGroup>
   </Project>

   Run dotnet build hybrasyl/Hybrasyl.csproj and confirm it builds against the local XML source (check build output for the project reference). Delete the file and confirm the NuGet path is restored.
3. Standalone ReadKey behavior (unchanged): Run dotnet hybrasyl/bin/.../Hybrasyl.dll --datadir <bad path> in a terminal to trigger World.Init() failure. Confirm the "Press any key to exit." message prints and the process waits for a keypress.
4. Redirected-stdin ReadKey behavior (new): Run the same command through a wrapper that pipes stdin (e.g. echo | dotnet hybrasyl/bin/.../Hybrasyl.dll --datadir <bad path> or launch via Epona's embedded mode). Confirm the process exits immediately with code 1, the fatal log line is still emitted, and no InvalidOperationException is thrown.
5. Run dotnet test — all existing tests stay green.

Impacted Areas in Hybrasyl

• Build configuration (hybrasyl/Hybrasyl.csproj, .gitignore) — conditional Hybrasyl.Xml reference
• Startup / world init failure path (hybrasyl/Game.cs) — fatal-exit console handling
• Documentation (docs/epona-branch-instances.md, docs/embedded-console-readkey-guard.md)
• No runtime, gameplay, networking, or data changes

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 30.90%. Comparing base (6d582aa) to head (a225216).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #326      +/-   ##
==========================================
+ Coverage   30.50%   30.90%   +0.40%     
==========================================
  Files         238      336      +98     
  Lines       25578    26215     +637     
  Branches     3513     3639     +126     
==========================================
+ Hits         7803     8103     +300     
- Misses      17137    17406     +269     
- Partials      638      706      +68     

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