feat: migrate ComfyUI nodes from presigned URLs to Brain API storage endpoints
## Core Architecture Changes
- Add new BrainApiClient for direct Brain API communication
- Replace presigned URL workflow with storage_id/filename pattern
- Update MediaStreamInput to use storage_id + filename instead of presigned_download_url
- Update MediaStreamOutput to use storage_id + filename instead of presigned_upload_url
## Brain API Client Implementation
- Add comprehensive BrainApiClient with authentication and error handling
- Implement get_presigned_upload_url() and get_presigned_download_url() methods
- Add proper Bearer token authentication for Brain API requests
- Include environment variable configuration for Brain API endpoint and credentials
## Media Stream Node Updates
- Refactor MediaStreamInput to request presigned URLs from Brain API using storage_id
- Update MediaStreamOutput to upload directly to MinIO using Brain API presigned URLs
- Simplify node interface by removing presigned URL inputs from workflow templates
- Update JavaScript frontend to hide system inputs and manage node UI state
## Infrastructure Improvements
- Add .idea/ to .gitignore for IDE file exclusions
- Update user_input.py to use new storage_id pattern
- Streamline web interface JavaScript for cleaner node management
- copy content_id, venue, canvas, scene from job payload into status updates
- use running_status for first progress; fail_status on execution errors (fallbacks preserved)
- manage per-content context lifecycles
Sly