Plan 3 smoke surfaced 'session_ended reason=error' on every wake with no
context. The relay now logs every upstream event type at INFO and forwards
any upstream 'error' event to the device as 'error code=upstream_<code>'
so it appears in the Pi's journal alongside the wake/session_ended pair.
Also extends the client's wakeword.predict with per-frame RMS + score
diagnostics and the bridge loop with a 5 s heartbeat for triage.
tes