Add output schema to MCP tools and expose MCP tool results in code mode

[pakrym-oai]

Summary

• drop McpToolOutput in favor of CallToolResult, moving its helpers to keep MCP tooling focused on the final result shape
• wire the new schema definitions through code mode, context, handlers, and spec modules so MCP tools serialize the exact output shape expected by the model
• extend code mode tests to cover multiple MCP call scenarios and ensure the serialized data matches the new schema
• refresh JS runner helpers and protocol models alongside the schema changes

Testing

• Not run (not requested)