agent: open Pi as a harness from the new-workspace dialog

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: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
7be7ab9701Lucenx9 committed on 10/5/2026, 5:53:04 PMparentce05ab1

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