Navigation guard misses redirect hops to private addresses #20

The SSRF guard from #18 checks the initial URL (assertPublicUrl) and every request seen by page.route('**/*'). Playwright only calls the route handler for the first URL in a redirect chain, so a public URL that redirects to a private or link-local address is followed without being checked.

Reproduction (appwrite/browser 0.3.5, Appwrite Cloud staging and production, 2026-10-04/05):

• /v1/avatars/screenshots?url=https://httpbin.org/redirect-to?url=http%3A%2F%2F169.254.169.254%2Flatest%2Fmeta-data%2F passes the API's URL validator (the initial host is public), and the browser follows the redirect to 169.254.169.254. The request timed out after 30s with nothing returned, apparently because the address isn't reachable from the pod. The guard did not stop it.
• A direct private URL, or a hostname that resolves privately (10.0.0.1.nip.io), is refused, but by the API's validator before the browser is involved.

Expected: every hop is checked with isPublicHost, and a redirect to a non-public host aborts the navigation (blockedbyclient).

Possible fix: in the route handler, fetch with redirects disabled (route.fetch({ maxRedirects: 0 })). On a 3xx, resolve Location against the request URL, check it with isPublicHost, and either abort or route.fulfill the redirect response so the browser re-requests the next hop, which passes through the handler again. Add a test with a public redirect to a private address.

Context: appwrite-labs/cloud#6236 (cloud runs 0.3.5 since 2026-10-05).