Fix the docs example for the snake_case rename

docs/http-api.md handed readers `result.structuredContent`, which raises
under mcp 2.x. Found by scanning the whole repo for attribute access on
SDK models rather than only the directories the last two fixes touched
-- that narrower sweep is what let CI find one before I did.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: soodoku

docs/http-api.md

@@ -106,7 +106,7 @@ async def main():
                     "data": {"y": [2.0, 4.1, 6.2], "x": [1, 2, 3]},
                 },
             )
-            print(result.structuredContent)
+            print(result.structured_content)
 ```
 
 ### Claude API (MCP connector)