fix(db): includes orderBy ignored after optimistic update on child collection

[comet08]

Closes #1444

🎯 Changes

When a child collection item is updated, the D2 graph emits a (-1, +1) pair. If the delete (-1) message arrives first, an accumulator entry is created with the old orderByIndex. The subsequent insert (+1) message updated value correctly but never updated orderByIndex — so the child collection's comparator kept using the stale positional index.

This caused incorrect sort order immediately after optimistic updates on child collections, with ordering only correcting itself after server confirmation.

The parent pipeline (accumulateChanges) already handled this correctly. This fix applies the same orderByIndex update logic to the child pipeline accumulator and the nested pipeline accumulator for consistency.

✅ Checklist

• I have tested this code locally with pnpm test.

🚀 Release Impact

• This change affects published code, and I have generated a changeset.
• This change is docs/CI/dev-only (no release).