feat: initialize repository structure and solution

Set up the PSProxmoxVE repository with solution file, project files for
Core library (net10.0+net48), PowerShell module, and xUnit test project.
Includes .gitignore, .editorconfig, LICENSE (MIT), CHANGELOG, and README
with supported version matrix and full cmdlet reference.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,12 @@
+bin/
+obj/
+TestResults/
+coverage/
+*.nupkg
+*.user
+*.suo
+.vs/
+nupkg/
+*.ps1xml.bak
+*.DotSettings.user
+BenchmarkDotNet.Artifacts/