Fix Happy Coder npm package name

Changed from incorrect `@happy-sdk/happy-coder` to correct `happy-coder`
package name. The scoped package doesn't exist on npm, causing Docker
build failures.

This fixes the v1.0.0 release Docker build.

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

Dockerfile

@@ -38,7 +38,7 @@ RUN curl -fsSL https://deb.nodesource.com/setup_lts.x | bash - && \
     rm -rf /var/lib/apt/lists/*
 
 # Install Happy Coder globally
-RUN npm install -g @happy-sdk/happy-coder
+RUN npm install -g happy-coder
 
 # Install Antigravity (Google's Project IDX / Cloud Code alternative)
 # Note: Antigravity might be packaged differently - adjust as needed