[savme]

This is a follow-up to #659. The 421 now fires for a hostname with no route on its own connection. The retry would land in the same place and get another 421.

The PR adjusts misdirect handling to account for hostnames with no routes.

Case	Main	This PR
Hostname with no route, own connection	421	404
Another site's hostname on a reused connection	421	421
Subdomain of a wildcard hostname that another gateway serves	421	421

Test plan

• Unit tests cover own hostnames, wildcard hostnames, overlapping gateways and listeners without a hostname.
• Lint passes on the extension server.
• The misdirected-request e2e scenario passes in the test env.

Related to #661