Python: [Python] Fix AG-UI endpoint missing request body schema and tags

[claude89757]

This commit addresses two issues with AG-UI FastAPI endpoint registration:

1. Request body schema for Swagger UI: Added AGUIRequest Pydantic model to define the request body structure. This enables proper OpenAPI schema generation, making the Swagger UI functional for testing AG-UI endpoints.

2. OpenAPI tags support: Added tags parameter to add_agent_framework_fastapi_endpoint() with a default value of ["AG-UI"]. This ensures endpoints are properly grouped in the OpenAPI documentation instead of falling into the "default" category.

Changes:

• Added AGUIRequest Pydantic model in _types.py with fields:
  • messages: AG-UI format messages
  • run_id: Optional run identifier
  • thread_id: Optional thread identifier
  • state: Optional shared state for agentic generative UI
• Modified add_agent_framework_fastapi_endpoint() to accept tags parameter and use AGUIRequest as the request body model
• Added DEFAULT_TAGS constant exported from the module
• Updated existing test for validation error handling (now returns 422)
• Added comprehensive tests for new functionality

🤖 Generated with Claude Code

Motivation and Context

Description

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

[claude89757]

@claude89757 please read the following Contributor License Agreement(CLA). If you agree with the CLA, please reply with the following information.

@microsoft-github-policy-service agree [company="{your company}"]

Options:

• (default - no company specified) I have sole ownership of intellectual property rights to my Submissions and I am not making Submissions in the course of work for my employer.

@microsoft-github-policy-service agree

• (when company given) I am making Submissions in the course of work for my employer (or my employer has intellectual property rights in my Submissions by contract or applicable law). I have permission from my employer to make Submissions and enter into this Agreement on behalf of my employer. By signing below, the defined term “You” includes me and my employer.

@microsoft-github-policy-service agree company="Microsoft"

Contributor License Agreement

@microsoft-github-policy-service agree