docs: expand AG-UI A2UI guide

[samjulien]

Summary

• add a top-level AG-UI + A2UI any-framework guide with AG-UI CLI setup, an app/framework selector, agent skills guidance, and framework-specific setup snippets
• add demo media for the guide: the top video defaults to the A2UI demo, switches to the Slack demo when Slack is selected, and is centered at 75% width on desktop
• update homepage, README, and nav labels so the original Quickstart and the any-framework guide are distinct

Notes

• The framework selector preserves the selected framework across MkDocs Material re-inits/hash navigation so TOC clicks do not reset the selected snippet.
• Framework-specific headings are styled as panel titles instead of Markdown headings so hidden framework panels do not appear in the TOC.

Verification

• npx --yes prettier@^3.5.0 --write docs/guides/a2ui-with-any-agent-framework.md
• git diff --check
• mkdocs build

[gemini-code-assist]

Code Review

This pull request updates the documentation to guide users on integrating A2UI with various agent frameworks and harnesses using AG-UI. It updates the README, index, and mkdocs configuration, and rewrites the integration guide to include a framework selector and code snippets for ADK, LangGraph, Mastra, Strands, CrewAI, Google Chat, Slack, and Teams. The review feedback highlights several issues in the new documentation, including incorrect relative asset paths, invalid Gemini model identifiers, and a nested list issue where a tool-retrieval function already returning a list was unnecessarily wrapped in another list.

[gemini-code-assist]

The relative path to the asset folder from docs/guides/a2ui-with-any-agent-framework.md should be ../assets/ instead of ../../assets/ because the file is located at a depth of two levels under the docs directory.

Suggested change

	<source src="../../assets/ag-ui-a2ui-demo.mp4" type="video/mp4">
	<source src="../assets/ag-ui-a2ui-demo.mp4" type="video/mp4">

[gemini-code-assist]

The relative path to the asset folder from docs/guides/a2ui-with-any-agent-framework.md should be ../assets/ instead of ../../assets/ because the file is located at a depth of two levels under the docs directory.

Suggested change

	<source src="../../assets/ag-ui-slack-demo.mp4" type="video/mp4">
	<source src="../assets/ag-ui-slack-demo.mp4" type="video/mp4">

[gemini-code-assist]

gemini-3.1-pro is not a valid Gemini model name. Since thinking_budget is configured, please use a model that supports thinking, such as gemini-2.0-flash.

Suggested change

	model="gemini-3.1-pro",
	model="gemini-2.0-flash",

[gemini-code-assist]

gemini/gemini-3.1-pro is not a valid Gemini model identifier in LiteLLM. Please use a valid model identifier such as gemini/gemini-2.0-flash.

Suggested change

	model="gemini/gemini-3.1-pro",
	model="gemini/gemini-2.0-flash",

[gemini-code-assist]

get_a2ui_tools returns a list of tools. Wrapping it in a list [a2ui_tool] creates a nested list [[tool1, tool2, ...]], which will cause issues when passed to ToolNode. Assign the returned list directly to TOOLS.

Suggested change

	a2ui_tool = get_a2ui_tools({"model": gemini})
	TOOLS = [a2ui_tool]
	TOOLS = get_a2ui_tools({"model": gemini})