chore: bump langsmith to ^0.8.0 (#2595)

## Description

The langsmith SDK published v0.8.0. This updates the `langsmith`
dependency in the workspaces that pin it via a caret range
(`langgraph-cli`) to `^0.8.0` and refreshes `pnpm-lock.yaml` so the
workspace packages resolve to `0.8.0`. The broad peer/dependency range
in `langgraph-api` (`>=0.5.19 <1.0.0`) already permits `0.8.0` and is
left unchanged, matching prior langsmith bump PRs. Transitive
`langsmith` versions pulled in by published `@langchain/*` packages are
left untouched.

## Test Plan
- [ ] `pnpm install --frozen-lockfile` resolves without changes

Made by [Open
SWE](https://openswe.vercel.app/agents/019f436f-3343-7169-a06a-5f64fe70e3af)

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Signed-off-by: Christian Bromann <git@bromann.dev>
Co-authored-by: Christian Bromann <731337+christian-bromann@users.noreply.github.com>
Co-authored-by: open-swe[bot] <open-swe@users.noreply.github.com>