Add Central Brain Agent Builder setup guide

[mmeola1134]

Pull Request Checklist

• I have read and followed the CONTRIBUTING.md guidelines.
• I have read and followed the Guidance for submissions involving paid services.
• My contribution adds a new instruction, prompt, agent, skill, workflow, or canvas extension file in the correct directory.
• The file follows the required naming convention.
• The content is clearly structured and follows the example format.
• I have tested my instructions, prompt, agent, skill, workflow, or canvas extension with GitHub Copilot.
• I have run npm start and verified that README.md is up to date.
• I am targeting the main branch for this pull request.

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Description

A standalone, self-contained HTML guide helps AT&T Microsoft 365 Copilot users build and test a personal Chief of Staff-style assistant in Agent Builder. It separates setup procedures from copy-ready prompts, provides step-by-step navigation between the walkthrough and prompt library, and includes an embedded hero image with an acknowledgment of the Viva Engage community that inspired the guide.

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Type of Contribution

• New instruction file.
• New prompt file.
• New agent file.
• New plugin.
• New skill file.
• New agentic workflow.
• New canvas extension.
• Update to existing instruction, prompt, agent, plugin, skill, workflow, or canvas extension.
• Other (please specify): Standalone HTML setup guide.

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Additional Notes

HTML parsing, inline JavaScript syntax, prompt navigation targets, embedded-image decoding, and git diff --check passed. npm start was attempted but could not run because js-yaml is not installed. npm ci was then attempted; dependency installation was blocked by local certificate validation (UNABLE_TO_GET_ISSUER_CERT_LOCALLY), so README generation could not be verified.

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By submitting this pull request, I confirm that my contribution abides by the Code of Conduct and will be licensed under the MIT License.