Fix CI git install test for fork PRs

Use `github.event.pull_request.head.repo.full_name` to correctly
reference the fork repository when testing git installs from PRs.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: jonathanhefner

.github/workflows/ci.yml

@@ -144,7 +144,7 @@ jobs:
           mkdir test-project
           cd test-project
           npm init -y
-          # Install from the PR branch
-          npm install "git+https://github.com/${{ github.repository }}#${{ github.head_ref || github.ref_name }}"
+          # Install from the PR branch (use head repo for fork PRs)
+          npm install "git+https://github.com/${{ github.event.pull_request.head.repo.full_name || github.repository }}#${{ github.head_ref || github.ref_name }}"
           # Verify the package is usable (ESM import)
           node --input-type=module -e "import { App } from '@modelcontextprotocol/ext-apps'; console.log('Import successful:', typeof App)"