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/default_config.py

@@ -17,6 +17,7 @@ _ENV_OVERRIDES = {
     "TRADINGAGENTS_MAX_RISK_ROUNDS":      "max_risk_discuss_rounds",
     "TRADINGAGENTS_CHECKPOINT_ENABLED":   "checkpoint_enabled",
     "TRADINGAGENTS_BENCHMARK_TICKER":     "benchmark_ticker",
+    "TRADINGAGENTS_TEMPERATURE":          "temperature",
 }
 
 
@@ -64,6 +65,11 @@ DEFAULT_CONFIG = _apply_env_overrides({
     "google_thinking_level": None,      # "high", "minimal", etc.
     "openai_reasoning_effort": None,    # "medium", "high", "low"
     "anthropic_effort": None,           # "high", "medium", "low"
+    # Sampling temperature, forwarded to every provider when set. None leaves
+    # each provider at its own default. Lower values reduce run-to-run
+    # variation on models that honor it; reasoning models largely ignore it
+    # and no setting makes LLM output bit-identical across runs (see README).
+    "temperature": None,
     # Checkpoint/resume: when True, LangGraph saves state after each node
     # so a crashed run can resume from the last successful step.
     "checkpoint_enabled": False,