docs: document webhook details page, delivery filters, and test action

[mintlify]

Summary

Document the new per-webhook details page, including delivery history, filters, payload/response inspection, and the Test Webhook action.

Changes

• Add an "Inspecting webhook deliveries" section covering the details page, the settings side panel, status/HTTP/event filters, expandable delivery rows (event ID, delivery ID, HTTP response, duration, error, payload), and Send test webhook.
• Update the "Save and Copy Secret" step to reflect that the list's row menu now only exposes Details and Delete, and the secret is copied from the details page.

Context

Follows #353, which introduced the dedicated webhook details page and removed secret from the /api/webhooks list response.

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Project	Deployment	Actions	Updated (UTC)
marble-web	Ready	Preview, Comment	Jun 16, 2026 8:12am

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