Fix environment variable passthrough and authentication improvements

[lroolle]

Issues Fixed

1. Environment Variables Not Passed to Non-root User

• XDG_CONFIG_HOME was exported but not passed through gosu
• Proxy settings, AWS credentials, and Anthropic settings were lost when switching to claude user
• Added comprehensive env var passthrough in docker-entrypoint.sh

2. Command Substitution Error

• Fixed error message with $(claude migrate-installer) which would execute non-existent command
• Changed to proper error message format

3. Authentication Method Improvements

• Added --auth-with pattern for cleaner auth selection
• Added note about using /login to switch from OAuth to API key
• Freed up -v flag for Docker volume mounting

4. Timezone Detection

• Added auto-detection of system timezone from /etc/localtime
• Fixes UTC default when running on macOS

5. Volume Mounting Support

• Added -v flag support to claude-yolo for custom volume mounts
• Follows Docker convention for volume syntax

Changes Made

• Enhanced build_gosu_env_cmd() to pass all necessary environment variables
• Fixed command substitution in error messages
• Added timezone auto-detection
• Improved authentication documentation
• Added flexible volume mounting support