Update Box plugin skills from upstream

[william-openai]

Important

Review-only mirror — do not merge this PR. The canonical Box plugin definition and release source now live in a private OpenAI-maintained repository. This public PR exists only so external Box collaborators can review the proposed skill content. Feedback from this review will be applied to the private canonical change.

Summary

• Sync the curated Box skills from box/box-for-ai@172a8273, the artifact shared by Box.
• Add the shared legal, contract-review, client-intake, and M&A deal-room skills included in that artifact.
• Replace the previous Box skill content and stale support files with the shared skill tree, add OpenAI launcher metadata for all five skills, and bump the plugin patch version from 0.0.3 to 0.0.4.

Curated adaptations

• Remove the shared skill's dependency on the Cursor-specific root rules/box.mdc file, which is not part of the OpenAI plugin bundle.
• Replace upstream npx skills add instructions and namespaced references with links to the skills already bundled in this plugin.
• Generalize Cursor- and Claude-specific callback and setup examples to client-neutral connector/MCP guidance.
• Preserve the existing OpenAI app binding, assets, marketplace entry, plugin interface metadata, and generic Box tool-selection guidance.