feat: add pptify plugin

[kimtth]

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.
• I am targeting the staged branch for this pull request.

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Description

Adds the pptify plugin for creating PowerPoint presentations from structured slide specifications.

PPTify includes a generated .agent runtime bundle with:

• PPTX generation tooling
• design context
• deck-generation workflow
• Copilot instructions
• policy guidance
• six runtime skills for context preparation, slide spec creation, deck generation, tooling, visual assets, and quality gates

The plugin source is maintained externally at:

https://github.com/kimtth/agent-pptify-kit

The submitted artifact was generated from that toolkit using its deploy artifact script and includes the runtime needed to create .pptx files, not only skill definitions.

Validation completed locally:

npm run plugin:validate
npm run build

Both commands completed successfully, and pptify was validated as a plugin.

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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

• The PR base branch has been updated from main to staged.
• This plugin intentionally includes the .agent runtime artifact because the skills alone cannot create PowerPoint files.
• Sample: pptify-kit-stress-demo.pptx — dense and intentionally overcomplicated layout used for stress testing PPTify output quality.
• Optional image generation uses user-provided OpenAI or Azure OpenAI credentials via .env; no credentials are included in this submission.

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

[github-actions]

⚠️ This PR targets main, but PRs should target staged.

The main branch is auto-published from staged and should not receive direct PRs.
Please close this PR and re-open it against the staged branch.

You can change the base branch using the Edit button at the top of this PR,
or run: gh pr edit 1826 --base staged