Add multi-model-review to community catalog

[formin]

Extension Submission

Extension Name: Multi-Model Review
Extension ID: multi-model-review
Version: 0.1.0
Author: formin
Repository: https://github.com/formin/multi-model-review

Description

Adds Multi-Model Review to the community catalog. The extension provides Spec Kit handoffs for using separate models for spec authoring, implementation routing, and review, with compact review packages built from Spec Kit artifacts and git diffs.

Checklist

• Valid extension.yml manifest
• README.md with installation and usage docs
• LICENSE file included
• GitHub release created (v0.1.0)
• Extension tested on real project structure
• All commands working
• No security vulnerabilities known
• Added to extensions/catalog.community.json
• Added to Community Extensions table in README.md

Testing

Tested on Windows PowerShell with the current spec-kit main checkout:

• Parsed extension.yml with Spec Kit's ExtensionManifest
• Verified all command files and command frontmatter parse correctly
• Verified local dev install with specify extension add --dev K:\dev\github\multi-model-review
• Verified release install with specify extension add multi-model-review --from https://github.com/formin/multi-model-review/archive/refs/tags/v0.1.0.zip
• Confirmed four speckit-multi-model-review-* Claude skill directories are registered
• Verified the release archive URL returns HTTP 200 after redirect
• Ran git diff --check

Additional Notes

This is a catalog and README registration PR only. The extension code is maintained in https://github.com/formin/multi-model-review.