Add AG-UI Channels page (Slack bots via CopilotKit Channels SDK)

[Markus Ecker (mme)]

Adds a new page under the AG-UI section: run the same Agent Framework AG-UI endpoint as a bot in Slack and other messaging platforms with the CopilotKit Channels SDK.

What changed

1. New page agent-framework/integrations/by-component/ui/ag-ui/channels.md. Covers how a channel fits together with an Agent Framework agent: the AG-UI server stays unchanged, and a separate long-running Node channel process — connected through CopilotKit Intelligence, which holds the Slack connection and credentials — drives the agent with HttpAgent from @ag-ui/client (the same client the Dojo uses for Agent Framework) and streams replies into the platform thread. Includes Slack setup via the Intelligence dashboard, other platforms, the message pipeline/credential split, and a durable-store production note.
2. All three pivots filled in. Step 1 (serve the agent over AG-UI) is pivoted for C# (MapAGUIServer), Python (add_agent_framework_fastapi_endpoint), and Go (aguiprovider.NewJSONHTTPHandler) — each mirroring the existing Getting Started / overview samples on port 8888. Steps 2–3 (the Node channel process) are shared across pivots since the channel connects to whatever AG-UI endpoint it's given.
3. TOC entry in agent-framework/toc.yml under UI > AG-UI ("Slack with CopilotKit Channels"), after Testing with Dojo.
4. Cross-links added to both Next Steps lists (C# and Python pivots) on the AG-UI overview page.

Verification

• Server snippets are taken from this repo's own Getting Started page (C#/Python) and AG-UI overview (Go), unchanged apart from trimming to the mapping call.
• The TypeScript channel snippet typechecks against the published @copilotkit/channels, @copilotkit/runtime, and @ag-ui/client npm packages.
• Frontmatter mirrors the sibling AG-UI pages (zone_pivot_groups: programming-languages, ms.service: agent-framework).

[learn-build-service-prod]

Learn Build status updates of commit bf9818b:

✅ Validation status: passed

File	Status	Preview URL	Details
agent-framework/integrations/by-component/ui/ag-ui/channels.md	✅Succeeded
agent-framework/integrations/by-component/ui/ag-ui/index.md	✅Succeeded

For more details, please refer to the build report.

[learn-build-service-prod]

Learn Build status updates of commit e219507:

✅ Validation status: passed

File	Status	Preview URL	Details
agent-framework/integrations/by-component/ui/ag-ui/channels.md	✅Succeeded
agent-framework/integrations/by-component/ui/ag-ui/index.md	✅Succeeded
agent-framework/TOC.yml	✅Succeeded

For more details, please refer to the build report.

[Markus Ecker (mme)]

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