fix: use camelCase structuredContent attr, prefer structured over text

- The MCP SDK Pydantic model uses camelCase (structuredContent), not
  snake_case (structured_content). The original getattr was a silent no-op.
- When structuredContent is present, return it AS the result instead of
  alongside text — the structured payload is the machine-readable data.
- Move test file to tests/tools/ and fix fake class to use camelCase.
- Patch _run_on_mcp_loop in tests so the handler actually executes.

tools/mcp_tool.py

@@ -1255,13 +1255,10 @@ def _make_tool_handler(server_name: str, tool_name: str, tool_timeout: float):
                     parts.append(block.text)
             text_result = "\n".join(parts) if parts else ""
 
-            # Preserve structured_content (structuredContent) if present
-            structured = getattr(result, "structured_content", None)
+            # Prefer structuredContent (machine-readable JSON) over plain text
+            structured = getattr(result, "structuredContent", None)
             if structured is not None:
-                return json.dumps({
-                    "result": text_result,
-                    "structuredContent": structured,
-                })
+                return json.dumps({"result": structured})
             return json.dumps({"result": text_result})
 
         try: