- Add __init__.py: support civitai.red domain and session token cookies
- Add core/downloader.py: build_download_headers for consistent User-Agent,
Accept, and CivitAI-specific Referer/Origin headers across download backends
- Resolve CivitAI API redirects before handing URLs to aria2
- Strip sensitive URL parameters from download logs
- Forward civitai_session_token from the frontend to the downloader