feat(example): add an example of tavily search

[wylswz]

Summary

Tool is a common use case of agent sandboxes. This PR demonstrated how SaaS tools can be integrated to OpenShell.

Related Issue

Changes

• Added an example of Tavily provider

Testing

• mise run pre-commit passes
• Unit tests added/updated
• E2E tests added/updated (if applicable)

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture docs updated (if applicable)

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