Fix deprecated mode attribute in README generator prompt

[daisukedd]

The mode attribute used in older OpenCode examples has been deprecated and replaced by agent.
Using mode causes parsing errors in current versions of OpenCode, while agent works as expected.
This PR updates the README generator prompt to remove the deprecated mode key and align the documentation with the updated OpenCode schema.

Before

mode: 'agent'
agent: 'agent'
description: 'Create a comprehensive README.md file for the project'

After

agent: 'agent'
description: 'Create a comprehensive README.md file for the project'

This improves accuracy, prevents configuration errors for users, and reflects the current agent configuration model described in the OpenCode documentation.

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Source	Review	Production	What Changed
copilot/tutorials/customization-library/prompt-files/create-readme.md	fpt ghec	fpt ghec

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[Copilot]

Pull request overview

This PR updates deprecated prompt file configuration syntax by replacing mode: 'agent' with agent: 'agent' in the README generator prompt example. The deprecated mode attribute causes parsing errors in current versions of OpenCode, and this change aligns the documentation with the current schema.

Key changes:

• Removed deprecated mode: 'agent' line from the YAML frontmatter in the README generator prompt example
• Retained agent: 'agent' as the correct configuration attribute

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[Copilot]

While this change correctly updates the deprecated mode: 'agent' to agent: 'agent', the same deprecated pattern exists in 5 other prompt file examples that should also be updated for consistency:

• content/copilot/tutorials/customization-library/prompt-files/document-api.md (line 26)
• content/copilot/tutorials/customization-library/prompt-files/generate-unit-tests.md (line 26)
• content/copilot/tutorials/customization-library/prompt-files/onboarding-plan.md (line 24)
• content/copilot/tutorials/customization-library/prompt-files/review-code.md (line 28)
• content/copilot/tutorials/customization-library/prompt-files/your-first-prompt-file.md (line 35)

Updating all occurrences in the same PR would ensure consistent documentation and prevent users from copying deprecated configurations from other examples.

[daisukedd]

@copilot open a new pull request to apply changes based on this feedback

[Nithin1044558]

[email protected]