Feature Request: Support multiple account login and switching (like `gh auth switch`)

Feature Request: Multiple Account Support / Account Switching

Problem

Users who work across multiple contexts (e.g., personal, Company A, Company B)
with separate Claude.ai accounts cannot quickly switch between them. There is
no way to see which account is currently active at a glance, and no fast
switching mechanism exists.

This creates real risks:

• Accidentally using a personal account for confidential company work
• Using a company account for personal projects (policy violation)
• No visual indicator of the currently active account in the workflow

Currently, switching requires a full logout → login cycle with browser
authentication every time, making it impractical to switch frequently.

Expected Behavior

Similar to gh auth switch in GitHub CLI:

• Store credentials for multiple accounts locally
• Switch accounts with a single command: claude auth switch
• Show the currently active account clearly (e.g., claude auth status)

Example Workflow

$ claude auth switch
? Select account:
  > personal@gmail.com (Personal - Pro)
    alice@company-a.com (Company A - Teams)
    alice@company-b.com (Company B - Teams)

Current Workaround

claude auth logout && claude auth login --email other@example.com

This triggers a full browser authentication flow every time.

Use Case

Freelancers, contractors, and consultants working across multiple
organizations need reliable, frictionless account switching to avoid
accidental cross-account usage.