feat: add backend for multiplayer support

backend/.gitignore

@@ -0,0 +1,56 @@
+## Build Folders
+bin/
+obj/
+out/
+
+## User-specific files
+*.user
+*.userosscache
+*.suo
+*.sln.docstates
+
+## Rider
+.idea/
+*.sln.iml
+
+## Visual Studio Code
+.vscode/
+
+## ASP.NET
+wwwroot/
+node_modules/
+dist/
+.env
+.env.*
+
+## Logs
+*.log
+logs/
+
+## Publish output
+publish/
+*.db
+
+## Test Results
+TestResults/
+*.trx
+*.coverage
+*.coveragexml
+
+## NuGet
+*.nupkg
+*.snupkg
+.nuget/
+packages/
+project.lock.json
+project.fragment.lock.json
+artifacts/
+
+## Temporary files
+*.tmp
+*.bak
+*.swp
+
+## OS Files
+.DS_Store
+Thumbs.db