Add extra_args support to deploy create command

- Add @click.argument for generic args passthrough to stack commands
- Keep explicit --network-dir and --initial-peers options
- Add DeploymentContext.get_compose_file() helper
- Add DeploymentContext.modify_yaml() helper for stack commands
- Update init() to use absolute paths

This allows stack-specific create commands to receive arbitrary
arguments via: laconic-so deploy create ... -- --custom-arg value

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

stack_orchestrator/deploy/deployment_context.py

@@ -44,11 +44,28 @@ class DeploymentContext:
     def get_compose_dir(self):
         return self.deployment_dir.joinpath(constants.compose_dir_name)
 
+    def get_compose_file(self, name: str):
+        return self.get_compose_dir() / f"docker-compose-{name}.yml"
+
+    def modify_yaml(self, file_path: Path, modifier_func):
+        """Load a YAML from the deployment, apply a modifier, and write back."""
+        if not file_path.absolute().is_relative_to(self.deployment_dir):
+            raise ValueError(f"File is not inside deployment directory: {file_path}")
+
+        yaml = get_yaml()
+        with open(file_path, "r") as f:
+            yaml_data = yaml.load(f)
+
+        modifier_func(yaml_data)
+
+        with open(file_path, "w") as f:
+            yaml.dump(yaml_data, f)
+
     def get_cluster_id(self):
         return self.id
 
-    def init(self, dir):
-        self.deployment_dir = dir
+    def init(self, dir: Path):
+        self.deployment_dir = dir.absolute()
         self.spec = Spec()
         self.spec.init_from_file(self.get_spec_file())
         self.stack = Stack(self.spec.obj["stack"])