Initialize batch upload session.

Creates a database-backed session for batch uploading images to an existing folder. Sessions expire after 24 hours and support up to 1000 files.

Security:

• Requires authentication (Bearer token)
• Rate limited to 10 requests/minute
• Validates folder exists and belongs to user

Request: - folder_id: UUID of existing folder (MUST exist before batch upload) - file_count: Number of images to upload (max 1000)

Response: - session_id: UUID for subsequent uploads (valid for 24 hours)

Workflow:

1. Validate user has org roles
2. Validate folder exists and belongs to user
3. Validate file_count <= 1000
4. Create database session with 24-hour TTL
5. Return session_id

Constraints:

• Maximum 1000 files per session
• Session expires after 24 hours
• Folder must exist before session creation
• Folder must belong to authenticated user