chore(examples): bump @langchain/* to v1, langsmith to ^0.6

LangChain.js released v1 stable; bashkit-js's own peer dep already
accepts v1 (>=0.3), and the langchain_agent.mjs example imports
DynamicStructuredTool / ChatOpenAI / createReactAgent — all still
exported from @langchain/{core,openai,langgraph} v1 with compatible
constructor signatures. Verified by running the example: it gets past
construction and fails at the OpenAI API call as expected when no key
is configured.

Also bumps the pinned langsmith override from 0.5.25 → ^0.6.0 to
match (and clear GHSA-3644-q5cj-c5c7 — already done in #1632 for
the maintenance branch; this PR keeps examples consistent).

Devdep change only — no source changes required.

Author: chaliy