Add Multi-Sites Spec Kit extension to community catalog

[mnriem]

Summary

• Adds the Multi-Sites Spec Kit extension to the community catalog
• Updates the community extensions documentation table

Extension

• Name: Multi-Sites Spec Kit
• ID: multi-sites
• Version: 1.0.0
• Author: teeyo

Validation

• Repository exists and is public
• extension.yml, README.md, and LICENSE are present
• Release tag v1.0.0 exists
• Download URL points to archive/refs/tags/v1.0.0.zip
• catalog.community.json validates as JSON

Closes #2770
cc @teeyo

[Copilot]

Pull request overview

Adds the “Multi-Sites Spec Kit” community extension to Spec Kit’s community extension catalog and documents it in the community extensions list, making it discoverable alongside other community-contributed extensions.

Changes:

• Added a new multi-sites entry to extensions/catalog.community.json with metadata (URLs, version, tags, requirements).
• Added “Multi-Sites Spec Kit” to the community extensions documentation table in docs/community/extensions.md.

Show a summary per file

File	Description
extensions/catalog.community.json	Registers the new community extension in the machine-readable community catalog.
docs/community/extensions.md	Adds the extension to the human-readable community extensions list for discoverability.

Copilot's findings

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• Files reviewed: 2/2 changed files
• Comments generated: 0

[mnriem]

Thank you!