Unified async upload - delegates to upload_pipeline().

Four usage scenarios:

1. Conversation upload: Provide conversation_id only (child_id inferred)
2. Standalone upload: Provide child_id only (no conversation link)
3. Explicit override: Provide both (rare edge case)
4. Infer conversation: Set infer_conversation=true with child_id (mobile chat)

REQUIREMENT: Must return 202 Accepted within 2 seconds Document processing happens asynchronously via worker queue

Authentication: JWT required via Authorization header RLS: Automatically enforced through user_client isolation

Args: files: List of files to upload (single or multiple) child_id: Optional UUID of child (inferred from conversation_id if not provided) conversation_id: Optional UUID linking to a conversation infer_conversation: Set to "true" to infer conversation_id from user's JWT idempotency_key: Optional key to prevent duplicate uploads on retry owned_by_note: Set to "true" when the files are being attached to a note, whose card draws them (see upload_pipeline) request: FastAPI request object for JWT authentication

Returns: 202 Accepted response with document_ids array and tracking information