chore(agent-toolkit): TypeScript 6.0 compatibility

[dstaley]

Description

This PR updates the @clerk/agent-toolkit package to be compatible with TypeScript 6.0 by migrating to tsdown.

Checklist

• pnpm test runs as expected.
• pnpm build runs as expected.
• (If applicable) JSDoc comments have been added or updated for any package exports
• (If applicable) Documentation has been updated

Type of change

• 🐛 Bug fix
• 🌟 New feature
• 🔨 Breaking change
• 📖 Refactoring / dependency upgrade / documentation
• other:

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
clerk-js-sandbox	Skipped		Mar 27, 2026 7:10pm

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Latest commit: 069a386

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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