Catalogue: Publish curated Canvas-only Agent Plugins

[gokhanarkan]

Summary

Track the curated Canvas-only Agent Plugin catalogue delivery implemented by PR #24.

Parent: https://github.com/github/github-app/issues/10216
Epic: https://github.com/github/copilot-ecosystem/issues/1230

Catalogue contract

Canvas-only packages keep the generic application/vnd.github.copilot-plugin media type and use the validated tags:

["canvas", "canvas-only", "github-copilot"]

canvas-only is valid only when the plugin has no useful non-Canvas agents, skills, hooks, or MCP servers.

Acceptance criteria

• At least five curated GitHub Copilot Canvas packages are represented; PR Add canvas-only plugins to catalog #24 adds 23.
• Entries use the generic Agent Plugin media type and the three required Canvas-only tags.
• Entries retain source repository/path provenance.
• Catalogue generation validates the tag/media-type contract and regenerates ai-catalog.json.
• Classification is explicit and does not depend on names, descriptions, or PR labels.
• PR Add canvas-only plugins to catalog #24 passes required checks and merges.
• A controlled type+tag query returns the Canvas-only entries for client integration.

Runtime/App consumption remains tracked separately by runtime #16831 and App #10216/#10217.