Memory-backed passport feed: grouped doc rows + standalone memories.

Single SQL UNION ALL: one row per documentId-with-memories (grouped on raw_document_id, joined to raw_documents for the status envelope) plus 1:1 standalone-memory rows (memories whose raw_document_id IS NULL). Sorted by (sort_at DESC, sort_id DESC); the webapp passport route consumes this as the memory-feed stream of its server-side two-stream merge. Cursor + limit semantics match the other document list routes; opaque next_cursor is the tuple of the last consumed row.