The hook now derives a unique mailbox name from the session_id supplied
on hook stdin, so two parallel Claude Code sessions in the same project
get distinct mailboxes (e.g. `claude-a8b3c1d2`, `claude-d4e5f6a7`)
instead of colliding on a shared env value. An optional
CLAUDE_MAILBOX_NAME base prefix flavors the names as `<base>-<sid>`.
Adds:
- `claude-mailbox session-announce` subcommand for the new SessionStart
hook, which prints the current session's mailbox name to context
- `/claude-mailbox:mailbox-update` slash command for `npm update` +
daemon restart
- stdin parsing helpers (parseHookStdin, deriveSessionName) with unit
tests; the doctor no longer needs a mandatory name prompt
Adds `install-hook` / `uninstall-hook` subcommands that idempotently patch
~/.claude/settings.json (or .claude/settings.json with --project), plus a
`--hook` flag on `check` that emits human-readable output and stays silent
on empty inbox or unreachable daemon.
