Pi gets its own AgentKind and adapter: process detection (pi sets
process.title, so /proc promotion works from a shell too) and
`pi --session <id>` resume. No hooks yet; status stays on the
terminal title/BEL signals.

Co-authored-by: Lucenx9 <185146821+Lucenx9@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 (1M context) <noreply@anthropic.com>