Implement shared CA certificate system for multi-server TLS security

- Generate shared CA during core deployment for consistent trust across servers
- Modify setup_docker_tls() to use shared CA instead of per-server CAs
- Update share_certs_with_core() to copy shared CA from core server
- Re-enable TLS verification (DOCKER_TLS_VERIFY=1) in Sablier
- Fix Sablier certificate mounting for proper TLS connection
- Add docker-tls/ to .gitignore to prevent certificate leaks
- Update documentation for shared CA approach

.gitignore

@@ -71,6 +71,9 @@ yarn-error.log*
 *.pfx
 acme.json
 
+# Docker TLS certificates directory
+docker-tls/
+
 # Nextcloud application files (should be mounted via volumes)
 docker-compose/productivity/nextcloud/html/