Update branding for Azure Copilot

[sdwheeler]

PR Summary

Update branding for Azure Copilot

• Fixes AB#506111

PR Checklist

• Descriptive Title: This PR's title is a synopsis of the changes it proposes.
• Summary: This PR's summary describes the scope and intent of the change.
• Contributor's Guide: I have read the contributors guide.
• Style: This PR adheres to the style guide.

[sdwheeler]

Hold for official announcement at Ignite.

[learn-build-service-prod]

PoliCheck Scan Report

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✅ No issues found

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[learn-build-service-prod]

Learn Build status updates of commit 12eb376:

✅ Validation status: passed

File	Status	Preview URL	Details
reference/docs-conceptual/AIShell/get-started/aishell-powershell.md	✅Succeeded	View (ps-modules)
reference/docs-conceptual/AIShell/get-started/aishell-standalone.md	✅Succeeded	View (ps-modules)
reference/docs-conceptual/AIShell/how-to/agent-azure.md	✅Succeeded	View (ps-modules)
reference/docs-conceptual/AIShell/how-to/aishell-reference.md	✅Succeeded	View (ps-modules)
reference/docs-conceptual/AIShell/overview.md	✅Succeeded	View (ps-modules)
reference/docs-conceptual/AIShell/release-notes.md	✅Succeeded	View (ps-modules)

For more details, please refer to the build report.