Capture deployment preview screenshots

[yuanzui-cf]

Objective

Show a Vercel-style screenshot for the current Production Deployment on the Project Overview page.

Scope

• Add an optional screenshot provider configuration with Chromium as the first provider.
• Drive the configured Chromium executable through the DevTools Protocol.
• Capture the deployment-specific platform preview origin and encode the final image as WebP.
• Store screenshots as deployment artifacts under the deployment object prefix.
• Add persisted capture jobs, retries, artifact delivery, and Overview loading and fallback states.

Acceptance Criteria

• Omitting screenshot configuration keeps capture disabled and preserves the globe and domain fallback.
• A configured Chromium provider captures a 16:9 preview without blocking or failing deployment delivery.
• Capture requests allow only the deployment same origin plus data and blob resources.
• Cross-origin resources are blocked by default.
• Failed captures retry with backoff and eventually use the existing fallback.
• Successful screenshots follow deployment artifact retention and migration behavior.
• The Overview shows a skeleton while capture is pending and the screenshot when ready.
• Backend and Console tests cover configuration, request isolation, retry state, artifact access, and UI states.

Constraints

• Do not use Playwright in the first implementation.
• Do not modify grass-output.zip.
• The provider interface must allow future online screenshot APIs without changing deployment storage contracts.
• Screenshot failures must never change deployment success or release state.