fix: add test fixture dependencies to CI workflow

Install react-markdown and remark-gfm packages required by
test/fixtures/markdown.js to resolve "Could not resolve" errors
during test execution in GitHub Actions.

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

Co-Authored-By: Claude <[email protected]>

Author: GSMLG-BOT

.github/workflows/test.yml

@@ -50,7 +50,7 @@ jobs:
           mix deps.get
 
       - name: Install JavaScript dependencies
-        run: bun install react@18 react-dom@18
+        run: bun install react@18 react-dom@18 react-markdown remark-gfm
 
       - name: Run tests
         run: mix test