fix(deepagents): align LangSmith sandbox create options with SDK (#528)

## Summary

This fixes a CI-breaking type mismatch in the LangSmith sandbox backend
introduced by the snapshot lifecycle update. `LangSmithSandbox.create()`
was using a `snapshotId` flow that did not match the current `langsmith`
SDK typings, which surfaced as unhandled Vitest typecheck errors in CI.