feat: add spec-kit-fixit extension to community catalog

[ismaelJimenez]

Description

Add the spec-kit-fixit community extension to the catalog. Fixit provides spec-aware bug fixing — maps bugs to spec artifacts, proposes a plan, and applies minimal changes.

Changes:

• Added fixit entry to extensions/catalog.community.json (alphabetical order)
• Added Fixit Extension row to the Community Extensions table in README.md
• Updated catalog updated_at timestamp to 2026-03-30

Testing

• Tested with a sample project (if applicable)

AI Disclosure

• I did use AI assistance (describe below)

AI was used to draft the fixit command.

[Copilot]

Pull request overview

Adds the new spec-kit-fixit community extension to Spec Kit’s community extension listings, keeping the extension catalog and documentation in sync.

Changes:

• Added a new fixit entry to extensions/catalog.community.json (kept in alphabetical order by extension id).
• Added a corresponding “Fixit Extension” row to the Community Extensions table in README.md.
• Bumped the community catalog updated_at timestamp to 2026-03-30T00:00:00Z.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
README.md	Adds Fixit to the Community Extensions table so users can discover it from the main docs.
extensions/catalog.community.json	Registers the Fixit extension metadata in the community catalog and updates the catalog timestamp.

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