fix: Resolve dead links in documentation files

- 02-memory/README.md: Remove broken example links, keep valid ones
- CONTRIBUTING.md: Fix relative path to SECURITY.md
- 07-plugins/README.md: Update MCP spec URL to working domain
- .github/SECURITY_REPORTING.md: Update OWASP link to valid cheatsheet
- .github/ISSUE_TEMPLATE/*: Replace placeholder links with comments
- .github/markdown-link-check-config.json: Add ignore patterns for
  example URLs in code blocks (docs.example.com, template files)

.github/ISSUE_TEMPLATE/documentation.md

@@ -41,4 +41,4 @@ How does this issue impact users?
 
 ## Related Documentation
 Links to related sections:
-- [Related Guide](link)
+- Related Guide: <!-- Add link here -->