Security documentation (#15242)

* Add comprehensive security documentation for SDL compliance

- Add security-configuration.md with MSBuild security settings and SDL compliance matrix
- Add security-best-practices.md with secure coding guidelines and Windows API usage
- Add security-process.md with security review process and compliance procedures
- Update README.md to include security documentation section

Addresses Work Item 59264836: SDL requirement for accessible security configuration guidance
Policy: Microsoft.Security.CE.10119 - Secure configuration guidance accessibility

* Change files

* fix(docs): Fix markdown linting errors in security documentation

- Fixed 126 markdown linting issues across 3 security documentation files
- Added blank lines around headings, lists, and code fences per MD022/MD031/MD032
- Removed trailing spaces and newlines per MD009/MD047
- All security docs now pass markdownlint-cli2 with 0 errors

Files fixed:
- docs/security-best-practices.md
- docs/security-configuration.md
- docs/security-process.md

Work Item: 59264836

* fix(docs): Correct security documentation links for vnext/README.md

- Changed paths from docs/ to ../docs/ to work from vnext directory
- vnext/README.md is auto-generated from root README.md during build
- Fixes link checker errors in CI build

---------

Co-authored-by: Nitin Chaudhary <[email protected]>

Author: Nitin-100

README.md

@@ -58,6 +58,10 @@ Search the [existing issues](https://github.com/microsoft/react-native-windows/i
 ## Documentation
 React Native has [great documentation](https://reactnative.dev/docs/getting-started). React Native for Windows adds its own separate [Windows and macOS documentation](https://microsoft.github.io/react-native-windows/) for desktop platform information like API docs and blog updates.
 
+### Security Documentation
+- **[Security Configuration Guide](https://github.com/microsoft/react-native-windows/blob/main/docs/security-configuration.md)** - Comprehensive guide for SDL-compliant security configurations
+- **[Security Best Practices](https://github.com/microsoft/react-native-windows/blob/main/docs/security-best-practices.md)** - Secure coding patterns and security API usage
+
 ### Examples
 - Using the CLI in the [Getting Started](https://microsoft.github.io/react-native-windows/docs/getting-started) guide will set you up with a sample React Native for Windows app that you can begin editing right away.
 - Check the [samples repo](https://github.com/microsoft/react-native-windows-samples) for more standalone samples.

change/react-native-windows-d0847c0c-28b9-4759-bc00-d287560bede3.json

@@ -0,0 +1,7 @@
+{
+  "type": "none",
+  "comment": "Add comprehensive security documentation for SDL compliance",
+  "packageName": "react-native-windows",
+  "email": "[email protected]",
+  "dependentChangeType": "none"
+}