feat(config): expose sampling temperature and document reproducibility

Adds a cross-provider temperature config (and TRADINGAGENTS_TEMPERATURE),
forwarded to every LLM client when set, so runs can be made less variable
on models that honor it. Adds a README "Reproducibility" section that
separates the sources of run-to-run variation, what users can control
(temperature, non-reasoning model, pinned date), and what is inherent to
LLM-driven analysis, and notes that the identity and verified-data fixes
already removed the "different companies / fabricated prices" variance.

#178 #168

tradingagents/llm_clients/azure_client.py

@@ -7,7 +7,7 @@ from .base_client import BaseLLMClient, normalize_content
 from .validators import validate_model
 
 _PASSTHROUGH_KWARGS = (
-    "timeout", "max_retries", "api_key", "reasoning_effort",
+    "timeout", "max_retries", "api_key", "reasoning_effort", "temperature",
     "callbacks", "http_client", "http_async_client",
 )