Pre-warm-up unknown-model warning + LiteLLM streaming hardening

Warn on bare unknown model names before warm-up. is_known_openai_bare_model
consults litellm.model_cost and matches only entries whose
litellm_provider == "openai". When the configured STRIX_LLM has no
provider prefix, isn't a known OpenAI model, and no LLM_API_BASE is
set, show a clear panel pointing the user at the <provider>/<model>
form and exit before issuing the doomed request — no more chasing an
"Incorrect API key" 401 from OpenAI when the user actually meant
deepseek/, anthropic/, etc. Custom-base configs are still allowed
through unconfirmed.

Disable LiteLLM's message-logging and streaming-logging knobs to cut
noise and skip one of the two end-of-stream submit paths. The other
path at streaming_handler.py:2206 schedules work on a global
ThreadPoolExecutor that loses to atexit shutdown when the interpreter
is winding down; the SDK's stream consumer surfaces that as a fatal
"cannot schedule new futures after shutdown" RuntimeError even though
the actual stream content was already delivered. Catch and swallow
that specific RuntimeError in _run_cycle so the scan isn't killed by
an upstream end-of-stream logging race.

strix/core/execution.py

@@ -349,12 +349,20 @@ async def _run_cycle(  # noqa: PLR0912
             )
             await coordinator.attach_stream(agent_id, stream)
             try:
-                async for event in stream.stream_events():
-                    if event_sink is not None:
-                        try:
-                            event_sink(agent_id, event)
-                        except Exception:
-                            logger.exception("stream event sink failed for %s", agent_id)
+                try:
+                    async for event in stream.stream_events():
+                        if event_sink is not None:
+                            try:
+                                event_sink(agent_id, event)
+                            except Exception:
+                                logger.exception("stream event sink failed for %s", agent_id)
+                except RuntimeError as stream_exc:
+                    if "after shutdown" not in str(stream_exc):
+                        raise
+                    logger.warning(
+                        "Ignoring LiteLLM end-of-stream shutdown race for %s",
+                        agent_id,
+                    )
                 if stream.run_loop_exception is not None:
                     raise stream.run_loop_exception
             finally: