ci: proper Agiliton deployment with health checks, rollback, smoke tests

- docker-compose.yml in repo (replaces inline generation in CI)
- /health nginx endpoint for container health checks
- HEALTHCHECK directive in Dockerfile
- CI pipeline: build → deploy → health check → smoke test → rollback on failure
- Smoke tests verify /health, /en/, /de/ after deploy
- Automatic rollback to previous image on health/smoke failure
- workflow_dispatch with force_deploy option
- Deploy-guard audit logging

IFK-6

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

nginx.conf

@@ -27,6 +27,13 @@ server {
         add_header Cache-Control "public, must-revalidate";
     }
 
+    # Health check endpoint
+    location /health {
+        access_log off;
+        return 200 "ok";
+        add_header Content-Type text/plain;
+    }
+
     # Redirect unprefixed paths to /en/
     location ~ ^/(?!en/|de/|css/|js/|img/|favicon|android|apple|site|llms) {
         return 302 /en$request_uri;