Phase G: scaffold .NET 10 + SignalR backend (engine port + hub + auth)

- server/ monorepo: Hokm.Engine (C# port of TS engine+AI, validated by sim),
  Hokm.Server (SignalR GameHub, in-memory matchmaking/rooms, server-side turn
  timers + bot fill + disconnect handling, per-seat state broadcast), Hokm.Sim
- JWT dev auth (OTP 1234 + email); CORS for the Next client; /hub/game
- NuGet restored from mirrors (Soroush Nexus + Liara); NuGetAudit off
- README + .NET .gitignore; static class Engine renamed Rules (namespace clash)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/Hokm.slnx

@@ -0,0 +1,9 @@
+<Solution>
+  <Folder Name="/src/">
+    <Project Path="src/Hokm.Engine/Hokm.Engine.csproj" />
+    <Project Path="src/Hokm.Server/Hokm.Server.csproj" />
+  </Folder>
+  <Folder Name="/tools/">
+    <Project Path="tools/Hokm.Sim/Hokm.Sim.csproj" />
+  </Folder>
+</Solution>