Targets broadcasts via per-tab list and open subs (validated at subscribe time)
instead of broadcasting message uuid to all agents. Adds frontend list typing, throttled sound,
and many perf improvements to reduce cpu memory & database queries.
Other fixes: Enforce message-to-conversation binding in handleGetMessage
- new vue app for serving live chat widget, created subdirectories inside frontend dir `main` and `widget`
- vite changes for both main app and widget app.
- new backend live chat channel
- apis for live chat widget