wip: capture for custom domains

[pory-gone]

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[iliasabk]

Security finding: the new allowlist validates only the initial URL returned by resolveCaptureTarget, but captureImage then calls page.goto(url.href) with normal redirect behavior and never revalidates the final/main-frame origin. If an ACTIVE custom-domain owner changes DNS before the domain is marked inactive and serves a valid HTTPS 30x response, the browser can be redirected to an origin that was never allowlisted (for example a localhost/link-local/internal HTTP endpoint), and the capture service will screenshot that destination. That makes the public capture endpoint an SSRF/screenshot primitive despite the initial hostname check.

Please enforce the boundary at browser-navigation time too: reject/abort main-frame navigation (including redirects and subsequent location changes) unless the destination remains the expected main/custom origin, and preferably reject private/link-local resolved addresses as defense in depth. A regression test with an allowlisted origin returning a 302 to a disallowed origin would cover the gap.