Eliminate dual accumulation by piggybacking assistant response text on
the server's ws_state:idle SSE event. The bridge no longer maintains
its own _ws_content_buffer — it reads content directly from the idle
event and passes it through to TurnCompleteEvent unchanged.
Server-side: WebUI accumulates tokens in on_content_token(), joins and
includes in the idle broadcast, then resets (with 256 KB cap).
Downstream consumers (Discord bidi DM forwarding, catch-up) are
unaffected — TurnCompleteEvent.content is still populated.
Patrick Buckley