feat(turn): self-hosted coturn support + time-limited creds + failure UX
- /api/ice: when TURN_SECRET is set, mint short-lived HMAC credentials
(coturn use-auth-secret) so no permanent password is exposed and the relay
can't be abused. Static TURN_USERNAME/CREDENTIAL still supported.
- share.html: connection watchdog + clear "couldn't connect on this network"
message instead of a blank screen when no path can be established.
- deploy/coturn: ready-to-run turnserver.conf + docker-compose + README for
hosting our own TURN on a VM we own (flat cost, no per-GB billing).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Sravan