fix: add tags support to workflow export and import

[davhparry]

The Workflow struct was missing a Tags field, causing tags to be silently dropped when deserialising the export API response and omitted when serialising the import request body.

Adds Tags []Tag to the Workflow struct, initialises it to an empty slice in NewWorkflow() to match the platform API behaviour of always returning "tags": [], and adds tests with real-world fixture data to verify tags are preserved through both export and import.

Description

Type of Change

• Bug fix
• New feature
• Documentation
• Refactor
• Chore

Changes Made

• pkg/services/workflows.go — Added Tags []Tag to the Workflow struct and initialised it to []Tag{} in NewWorkflow() so an empty tags array is always serialised as "tags": [], matching the platform API behaviour
• pkg/services/workflows_test.go — Added TestWorkflowExportPreservesTags and TestWorkflowImportPreservesTags to verify tags are preserved through both operations
• pkg/services/testdata/.../export.with-tags.success.json — New export fixture with a real-world tag object
• pkg/services/testdata/.../import.with-tags.success.json — New import fixture with a real-world tag object

Testing

Unit tests added for export and import with tags
done
Full test suite passes (make test)
done
Manually verified with a real workflow — export now includes tags when present and "tags": [] when not, matching platform API output

Checklist

• Code follows the project's style guidelines
• Self-review of code has been performed
• Code has been commented where necessary
• Tested with make setup or relevant profile
• Commits follow conventional format (type: subject)
• No secrets or credentials committed
• Documentation has been updated accordingly
• PR has been labeled appropriately (enhancement, bug, documentation, refactor, chore)

Related Issues

Closes # 200