docs: webhooks docs

[RomneyDa]

Description

Docs for webhook cloud agents

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Summary by cubic

Added a new Webhooks docs page for Cloud Agents covering setup, authentication, integrations (Zapier, GitHub Actions, cURL), API details, troubleshooting, and example agent prompts. Updated docs navigation to include the Webhooks page.

^{Written for commit 06ebb6fdd8ef5d3401e40a164f8d2f7dda25e00e. Summary will update automatically on new commits.}