Ingest documents (text, files, or mixed)

Unified document ingestion endpoint.

Accepts a multipart form with:

• manifest (required): JSON array describing each item
• files (optional): one or more file uploads, referenced by file_index in the manifest

Manifest format (JSON array):

[
  {"type": "file", "file_index": 0, "title": "Report"},
  {"type": "text", "title": "FAQ", "content": "What is..."},
  {"type": "file", "file_index": 1, "title": "Old Report", "document_id": "uuid"}
]