- coreReady now only flips after the embedded core actually answers HTTP
(fixes blank-screen race where the iframe loaded before the listener)
- renderer probes reachability, retries frame load with exponential backoff,
and recovers via onerror instead of giving up forever
- keep per-user theme in localStorage
- embedded profile no longer preconfigures a zen source (desktop users add
their own upstreams on the sources page)