fix(ci): require docker-capable Jenkins agent with preflight checks

docs/deployment-production.md

@@ -109,6 +109,14 @@ Configure these values in Jenkins job/folder/global environment or credentials-b
 
 The pipeline assumes Jenkins credentials are managed outside this repository.
 
+Jenkins runtime requirements:
+
+- The pipeline must run on a Jenkins agent with the `docker` label.
+- That agent must have Docker CLI installed and permission to access Docker daemon/socket.
+- `rsync` and `ssh` must also be available on the Jenkins agent.
+
+If Docker is missing or inaccessible, the pipeline now fails early in a dedicated preflight stage with an explicit message.
+
 ## Deploy flow
 
 Deployment is intentionally simple and bash-based: