New environment variables passed through to host apps and child processes

Environment variables are settings given to a program through its shell. Claude Code passes some of them on to programs it starts or that host it. These were added to those lists:

• CLAUDE_CODE_HOST_PROMPT_SUPERSEDES_RECORD, passed to host apps and child processes. In print mode (-p), it also sets an internal setting, which is reset when no system prompt has been set
• CLAUDE_CODE_MCP_SERVE_SETTINGS, passed to child processes
• CLAUDE_CODE_DISABLE_WEB_FETCH, added to a list of variables passed through