[DOCS] Document CLAUDE_CONFIG_DIR environment variable for multi-account setups

Documentation Type

Missing documentation (feature not documented)

Documentation Location

_No response_

Section/Topic

Enironment variables for claude command

Current Documentation

_No response_

What's Wrong or Missing?

Summary

The CLAUDE_CONFIG_DIR environment variable can be used to specify an
alternative configuration directory instead of the default ~/.claude/.
However, this is not documented anywhere — not in claude --help, not
in the official docs.

## Use Case

Users who have multiple claude.ai accounts (e.g. work and personal) can
use this variable to maintain separate configurations and switch between
accounts without affecting the rest of their environment:

```bash
# Add to ~/.zshrc
alias claude-personal='CLAUDE_CONFIG_DIR=~/.claude-personal claude'

# Login with the second account
CLAUDE_CONFIG_DIR=~/.claude-personal claude auth login

  This is far simpler and safer than overriding $HOME, which would affect
  git, ssh, and other tools invoked by Claude Code.


### Suggested Improvement


  Request

  Please add CLAUDE_CONFIG_DIR to:
  - claude --help output
  - Official documentation (configuration / authentication section)

  This would make multi-account usage straightforward for all users.


### Impact

Low - Minor confusion or inconvenience

### Additional Context

This text is reported by claude code himself.