feat: initial project structure with Snake.Core, CLI and Avalonia skeleton

.gitignore

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+## Ignore Visual Studio temporary files, build results, and
+## files generated by popular Visual Studio add-ons.
+
+*.rsuser
+*.suo
+*.user
+*.userosscache
+*.sln.docstates
+
+*.userprefs
+
+## Mono auto generated files
+mono_crash.*
+
+## Build results
+[Dd]ebug/
+[Dd]ebugPublic/
+[Rr]elease/
+[Rr]eleases/
+x64/
+x86/
+[Ww][Ii][Nn]32/
+[Aa][Rr][Mm]/
+[Aa][Rr][Mm]64/
+bld/
+[Bb]in/
+[Oo]bj/
+[Ll]og/
+[Ll]ogs/
+
+## Visual Studio cache/options directory
+.vs/
+
+## MSTest test Results
+[Tt]est[Rr]esult*/
+[Bb]uild[Ll]og.*
+
+## NUnit
+*.VisualState.xml
+TestResult.xml
+nunit-*.xml
+
+## .NET Core
+project.lock.json
+project.fragment.lock.json
+artifacts/
+
+## NuGet Packages
+*.nupkg
+*.snupkg
+**/[Pp]ackages/*
+!**/[Pp]ackages/build/
+
+## Rider
+.idea/
+*.sln.iml
+
+## VS Code
+.vscode/
+
+## OS generated files
+.DS_Store
+Thumbs.db
+
+## Avalonia
+*.DotSettings.user