Add browser.relayBindHost config option so the Chrome extension relay
server can bind to a non-loopback address (e.g. 0.0.0.0 for WSL2).
Defaults to 127.0.0.1 when unset, preserving current behavior.
Closes#39214
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>