#30 [highway-api] Implement Artifact Manager UI for uploading Python code as zip files

Add artifact management feature to the Highway UI that allows users to: 1. Write/paste Python code in the UI 2. Upload code as a zip file 3. Get an artifact ID for the uploaded code 4. View/manage existing artifacts 5. Associate artifacts with workflow tasks This is critical for enabling custom Python activities in workflows without requiring CLI access. Requirements: - Upload interface for zip files - Code editor for writing Python directly - Artifact listing/management page - Integration with workflow task configuration - Artifact versioning support