Fix code-server installation with explicit path and verification

- Use standalone method with /usr/local prefix for clear installation path
- Add verification step to ensure code-server is properly installed
- Build will now fail if code-server installation fails

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

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

Dockerfile

@@ -63,7 +63,8 @@ RUN apt-get install -y fcitx5 --fix-missing
 RUN apt-get clean && rm -rf /var/lib/apt/lists/*
 
 ## code server
-RUN curl -fsSL https://code-server.dev/install.sh | sh
+RUN curl -fsSL https://code-server.dev/install.sh | sh -s -- --method standalone --prefix=/usr/local
+RUN which code-server && code-server --version
 
 ## PlayWright Chrome
 RUN npx playwright install chrome