Create Document Group Endpoint

Create a document group.

Request body: name: Group name (e.g., "Proof of Address") description: Optional description classifications: List of classification slugs this group handles extraction_config: Optional extraction config check_config: Optional check suite override recency_config: Optional recency rules (e.g., {"max_age_days": 90, "enabled": true}) is_default: Whether this is the fallback group priority: Match priority (higher = checked first)