Add Architect Impact Previewer extension to README

Author: UmmeHabiba1312

README.md

@@ -183,6 +183,7 @@ The following community-contributed extensions are available in [`catalog.commun
 | Extension | Purpose | Category | Effect | URL |
 |-----------|---------|----------|--------|-----|
 | AI-Driven Engineering (AIDE) | A structured 7-step workflow for building new projects from scratch with AI assistants — from vision through implementation | `process` | Read+Write | [aide](https://github.com/mnriem/spec-kit-extensions/tree/main/aide) |
+| Architect Impact Previewer | Predicts architectural impact, complexity, and risks of proposed changes before implementation. | `visibility` | Read-only | [spec-kit-architect-preview](https://github.com/UmmeHabiba1312/spec-kit-architect-preview) |
 | Archive Extension | Archive merged features into main project memory. | `docs` | Read+Write | [spec-kit-archive](https://github.com/stn1slv/spec-kit-archive) |
 | Azure DevOps Integration | Sync user stories and tasks to Azure DevOps work items using OAuth authentication | `integration` | Read+Write | [spec-kit-azure-devops](https://github.com/pragya247/spec-kit-azure-devops) |
 | Branch Convention | Configurable branch and folder naming conventions for /specify with presets and custom patterns | `process` | Read+Write | [spec-kit-branch-convention](https://github.com/Quratulain-bilal/spec-kit-branch-convention) |