feat: add Claude Code image support (#16)

* feat: add Claude Code image support

Add a new Cubbi image for Claude Code (Anthropic's official CLI) with:
- Full Claude Code CLI functionality via NPM package
- Secure API key management with multiple authentication options
- Enterprise support (Bedrock, Vertex AI, proxy configuration)
- Persistent configuration and cache directories
- Comprehensive test suite and documentation

The image allows users to run Claude Code in containers with proper
isolation, persistent settings, and seamless Cubbi integration. It
gracefully handles missing API keys to allow flexible authentication.

Also adds optional Claude Code API keys to container.py for enterprise
deployments.

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

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

* Pre-commit fixes

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Your Name <you@example.com>

cubbi/container.py

@@ -203,6 +203,8 @@ class ContainerManager:
             api_keys = [
                 "OPENAI_API_KEY",
                 "ANTHROPIC_API_KEY",
+                "ANTHROPIC_AUTH_TOKEN",
+                "ANTHROPIC_CUSTOM_HEADERS",
                 "OPENROUTER_API_KEY",
                 "GOOGLE_API_KEY",
                 "LANGFUSE_INIT_PROJECT_PUBLIC_KEY",