v0.4.0 — Multi-account credentials + Auto-update

Added

• Multi-account credential support — manage multiple Linear accounts and switch
  between them automatically per workspace or via explicit --account flag.
  • New config schema: [accounts.<name>] sections with token, token_env,
    and auto-populated org_name.
  • Workspace-aware defaults: git repository roots can be mapped to specific
    accounts via config.toml [workspaces] or automatically detected.
  • New clinear auth subcommands:
    • auth accounts — list all accounts with default/workspace/current markers
    • auth add <name> --token <token> — add a named account (optionally
      verifies token against Linear API to populate org_name)
    • auth switch <name> — set global default account
    • auth remove <name> — remove an account
    • auth workspace — show current git repo workspace and mapped account
  • New global flag: --account <name> / -a <name> — one-off override for
    any subcommand.
  • Backward compatibility: existing [auth] sections auto-migrate to
    accounts.default on first load. Single-account behavior is preserved
    as fallback.
• clinear update — self-update command that checks PyPI for the latest
  version and runs the appropriate upgrade command (pip install --upgrade or
  pipx upgrade). Supports --dry-run and --yes flags. JSON output mode
  supported for agent consumption.
• New dependency: tomli-w>=1.0 (required for writing config updates from
  auth add/switch/remove commands).

Changed

• config.py — replaced single AuthConfig with AccountConfig and
  AccountsConfig dict. Added resolve_account() for workspace-aware
  account selection and save_config() for persisting config changes.
• cli_state.py — added account_name field to CLIState for tracking
  the active account.
• cli.py — added --account global flag and update command registration.
• init.py — updated config template to use multi-account schema.

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