Add docs link in sidebar, Dockerfile for VitePress, make Keycloak optional

- Add external "Docs" link in sidebar with configurable DOCS_URL
- Add Dockerfile.docs for VitePress static site (nginx)
- Add DOCS_URL build arg to Dockerfile.dashboard
- Run cargo fmt

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

compliance-dashboard/src/infrastructure/keycloak_config.rs

@@ -52,4 +52,3 @@ impl KeycloakConfig {
         )
     }
 }
-