fix(deploy): merge volumes from stack init() instead of overwriting

Previously, volumes defined in a stack's commands.py init() function
were being overwritten by volumes discovered from compose files.
This prevented stacks from adding infrastructure volumes like caddy-data
that aren't defined in the compose files.

Now volumes are merged, with init() volumes taking precedence over
compose-discovered defaults.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

stack_orchestrator/deploy/deployment_create.py

@@ -469,7 +469,10 @@ def init_operation(
                 # Docker Compose and kind: use relative paths
                 volume_descriptors[named_volume] = f"./data/{named_volume}"
         if volume_descriptors:
-            spec_file_content["volumes"] = volume_descriptors
+            # Merge with existing volumes from stack init()
+            # init() volumes take precedence over compose defaults
+            orig_volumes = spec_file_content.get("volumes", {})
+            spec_file_content["volumes"] = {**volume_descriptors, **orig_volumes}
         if configmap_descriptors:
             spec_file_content["configmaps"] = configmap_descriptors