feat: add additional security enhancements (Issue #365)

- Add constant-time token comparison utility (crypto/subtle)
- Add SBOM generation and attestation to CI/CD pipeline
- Document TLS enforcement, DNS security (DoH/DoT), and container hardening
- Create Security Incident Response Plan (SIRP)
- Add security update notification documentation

Security enhancements:
- Mitigates timing attacks on invite token validation
- Provides supply chain transparency with CycloneDX SBOM
- Documents production container hardening (read_only, cap_drop)

Closes #365

.github/workflows/docs-to-issues.yml

@@ -17,7 +17,7 @@ on:
       dry_run:
         description: 'Dry run (no issues created)'
         required: false
-        default: 'false'
+        default: false
         type: boolean
       file_path:
         description: 'Specific file to process (optional)'