Initial plan and README for Windows webhook server

Empty project scaffolded with the approved implementation plan,
README overview, and a .NET-appropriate .gitignore. Implementation
will follow on a Windows machine.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,47 @@
+# Build output
+bin/
+obj/
+out/
+publish/
+*.user
+*.suo
+*.userprefs
+
+# Visual Studio / Rider / VS Code
+.vs/
+.vscode/
+.idea/
+*.swp
+
+# Test results
+TestResults/
+*.trx
+*.coverage
+*.coveragexml
+
+# NuGet
+*.nupkg
+*.snupkg
+.nuget/
+packages/
+project.lock.json
+project.assets.json
+
+# DotNet tooling
+.dotnet/
+
+# Logs / config produced at runtime (not source)
+logs/
+*.log
+config.local.json
+
+# OS
+.DS_Store
+Thumbs.db
+
+# Secrets — never commit these
+*.pfx
+*.p12
+*.key
+secrets.json
+appsettings.*.local.json