feat: carry the reasoning verdict through to LLMResponse

Both assembly paths fill it, streaming and non-streaming alike. Filling
only one is exactly the divergence this issue exposed: M3 returns
reasoning prose over SSE and nothing at all over the plain endpoint, so
a verdict computed on one path says nothing about the other.

The field defaults to UNKNOWN on both TransportResult and LLMResponse.
A transport that does not judge should not get to declare absence on
the provider's behalf, and a default that stays silent is the only one
that cannot lie.

src/polygateway/middleware/retry.py

@@ -390,6 +390,8 @@ class RetryMW:
             cached_prompt_tokens=result.cached_prompt_tokens,
             model_reported=result.model_reported,
             reasoning_tokens=result.reasoning_tokens,
+            # 裁定归 transport(它才见得到原始信号),本层只搬运不改判
+            thinking_observation=result.thinking_observation,
         )
 
     async def _emit(