notion-react: relocating a cached <ChildPage> under a brand-new parent recreates it instead of moving

Problem

The cross-parent move detection (pagesByKey + movePage) only runs inside diffChildren recursions over existing scopes. When a cached <ChildPage> is relocated under a brand-new parent (new page, toggle, or column), the new subtree is built by emitAppendsForNew / inlinePackChildren, which tail a fresh createPage for every page-kind candidate without consulting the cache. The old location then emits archivePage (the move is also not pre-claimed, since collectPreClaimedMoves does not descend into unretained candidates).

Net effect: the page identity churns (archive + recreate), server-side content is duplicated transiently, and any checkpointed pending state from #1100 is adopted but then discarded.

Repro sketch

1. Warm sync <Page><A/><ChildPage k="c"/></Page>.
2. Re-sync with <Page><A/><Toggle><ChildPage k="c"/></Toggle></Page> (toggle is new).
3. Observe createPage(c) + archivePage(c-old) instead of movePage(c → toggle).

Suggested direction

• Teach emitAppendsForNew and the inlinePackChildren tail path to emit movePage (parent = tmp id, resolved at apply time) when a page-kind candidate's key exists in pagesByKey.
• Extend collectPreClaimedMoves to recurse into unretained candidate subtrees so the outgoing parent skips the archive.
• Recurse content reconciliation into moveSource.children vs the candidate subtree after the move.

Related: #1100 (pending page-create checkpoints) — its adoption now runs before cross-parent matching, so this gap is the remaining convergence hole for relocated pages.

Start with emitAppendsForNew, the inlinePackChildren tail path, and collectPreClaimedMoves, then trace pagesByKey and movePage through the existing diffChildren logic. Reproduce the new-parent Toggle case described in the issue and inspect how moveSource.children is reconciled. Done means the cached page uses movePage, the old location skips archivePage, and the page is not recreated.