addresses two issues in the WebRTC same-LAN test:
1. "Cannot set remote answer in state stable" on retry
the offerer's pc enters stable after the first successful accept-
answer; subsequent clicks fail. add a reset-connection button that
close()s the current pc, clears all SDP textareas + status lines,
detaches inbound rx decoders, & restores the disconnected UI.
user can now retry without reloading the page.
2. silent NAT/mDNS diagnostic gap
browsers anonymize host IPs as <uuid>.local mDNS names. routers
with multicast-blocking client isolation (common on guest Wi-Fi)
silently prevent host-candidate pairing on the same LAN. add:
* a details/summary section under the rtc dot documenting the
Firefox + Chromium config knobs to disable host obfuscation;
* pc.onicecandidate logging that prints candidate type
(host/srflx/relay) + an explicit '(mdns-anonymized)' tag
for .local foundations, so the user can see WHAT is being
gathered without opening devtools;
* an err logLine on connectionState=failed pointing at the
reset button.
unchanged: protocol, frame codec, crypto, audio path, signaling
flow. UI surface gains one button + one collapsed details panel.