feat: add VS Code devcontainer support

[franccesco]

Summary

• Add comprehensive VS Code devcontainer configuration for consistent development environment
• Include essential developer tools: uv, GitHub CLI, Claude Code, direnv, and zsh
• Automate environment setup with post-create script

Key Features

• Docker-based development: Python 3.12 container with all necessary dependencies
• VS Code integration: Pre-configured extensions (Python, Pylance, Ruff, Claude Code)
• Developer tools: GitHub CLI for PR management, Claude Code for AI assistance
• Environment automation: direnv for automatic virtual environment activation
• Enhanced shell: Zsh with Oh My Zsh for better terminal experience
• Post-create setup: Automatic dependency installation and optional GitHub authentication

Test Plan

• Clone repository and open in VS Code with Dev Containers extension
• Verify container builds successfully
• Confirm all tools are installed and accessible (uv, gh, claude, direnv)
• Test automatic virtual environment activation with direnv
• Verify Python development workflow (pytest, ruff, pyright)
• Test GitHub CLI authentication flow
• Ensure VS Code extensions are installed and configured