feat(agents): rename to sentiment_analyst; integrate StockTwits + Reddit

Pre-fetches news + StockTwits + Reddit via no-auth public endpoints
and injects structured data blocks into the prompt with professional
analysis instructions. Replaces the prompt-vs-tool mismatch that
caused fabricated social-platform content. Backward-compat alias +
"social" CLI key preserved.

#557 #607

tradingagents/graph/setup.py

@@ -54,7 +54,11 @@ class GraphSetup:
             tool_nodes["market"] = self.tool_nodes["market"]
 
         if "social" in selected_analysts:
-            analyst_nodes["social"] = create_social_media_analyst(
+            # "social" selector key preserved for back-compat with existing
+            # user configs; the underlying agent has been renamed to
+            # sentiment_analyst (the old name advertised social-media data
+            # the agent never had access to — see issue #557).
+            analyst_nodes["social"] = create_sentiment_analyst(
                 self.quick_thinking_llm
             )
             delete_nodes["social"] = create_msg_delete()