[maxy-shpfy]

Description

Surface the remote host environments connected to a session in the participants sidebar. Adds a GET /sessions/:id/environments route backed by remoteEnvironmentGateway.listEnvironments, a useSessionEnvironments query hook, and an EnvironmentRow rendered in the participants list/window. Extends packages/shared/src/contracts.ts with the environment-summary shape.

How to test

1. Run pnpm dev.
2. Connect a remote environment to a session.
3. Open the participants panel and confirm the environment appears with its tool/sub-agent counts.

Notes

First PR in the remote-environments stack (#107 → #113).

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