Update agent frontmatter options to remove deprecated "infer"

[Anddd7]

• Removed 'infer' option and replaced it with 'user-invocable' and 'disable-model-invocation'.
• Clarified the purpose of new options for better usability.
• Updated guidelines to reflect changes in agent invocation behavior.

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, or workflow 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, or workflow with GitHub Copilot.
• I have run npm start and verified that README.md is up to date.

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Description

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Type of Contribution

• New instruction file.
• New prompt file.
• New agent file.
• New plugin.
• New skill file.
• New agentic workflow.
• Update to existing instruction, prompt, agent, plugin, skill, or workflow.
• Other (please specify):

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Additional Notes

https://code.visualstudio.com/docs/copilot/customization/custom-agents#_custom-agent-file-structure

infer | Deprecated. Use user-invocable and disable-model-invocation instead. Previously, infer: true (the default) made the agent both visible in the picker and available as a subagent. infer: false hid it from both. The new fields give you independent control: use user-invocable: false to hide from the picker while still allowing subagent invocation, or disable-model-invocation: true to prevent subagent invocation while keeping it in the picker.

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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.

[Copilot]

Pull request overview

Updates the custom agent authoring guidelines to reflect the deprecation of the infer frontmatter flag and document the newer agent-invocation controls.

Changes:

• Removed infer from the frontmatter example.
• Documented user-invocable and disable-model-invocation options and their defaults.
• Updated the agent creation checklist to reference the new invocation controls.