Initial import of the CBDDC codebase with docs and tests. Add a .NET-focused gitignore to keep generated artifacts out of source control.

SECURITY.md

@@ -0,0 +1,18 @@
+# Security Policy
+
+## Supported Versions
+
+| Version | Supported          |
+| ------- | ------------------ |
+| 1.0.x   | :white_check_mark: |
+| < 1.0   | :x:                |
+
+## Reporting a Vulnerability
+
+If you discover a security vulnerability in CBDDC, please **DO NOT** open a public issue.
+
+Instead, please report it via privacy-preserving means:
+- Email the maintainers directly (if contact info is available).
+- Or use GitHub's "Report a vulnerability" feature if enabled.
+
+We will make every effort to acknowledge your report within 48 hours and provide a timeline for a fix.