feat: add stable-id rebase tracer

[developer-1px]

Summary

• add a private stable-id-rebase lab that materializes one delayed field replacement against the current Pointer of a host-owned stable id
• bind the official id resolver to the supplied document, preserving remote moves, reorders, and unrelated edits while rejecting stale authored values
• guard the current entity and expected field value so planning-to-commit races fail atomically
• verify preview identity with the configured readId, rebase one relative selection, and preflight the complete plan through public schema semantics
• extend lab evaluation to support declared official-extension peers and rebuild those peers before verification
• keep the JSONDocument public API unchanged; transport, clocks, OT, CRDT, convergence, and replicated undo remain explicit non-goals

Validation

• npm run labs:extensions:verify:changed -- --base origin/main --head HEAD (40/40 labs verified)
• npm run docs:evaluate
• pre-push core build
• git diff --check