Cursor stack pagination

Chose a persisted JSON stack of opaque page-start cursors over recomputing cursors because APIs expose forward-only tokens while the CLI supports -c next and -c prev. Use paginationHint() with prebuilt previous/next hints, expose hasPrev and nextCursor in JSON, truncate stale later cursors after backtracking, and stop auto-pagination at the requested limit, cursor exhaustion, or MAX_PAGINATION_PAGES.