Browser migration

The old in-process browser tool has moved to Rig. Rig keeps the semantic ARIA-first interaction model, but the headful browser and persistent profile now live on a dedicated machine beside Outpost rather than inside each Kin session.

When Rig is configured, browser remains a dispatch-only alias for rig, so old journals and familiar prompts continue to work. New prompts see rig. The legacy browser_enabled and browser_allow_private settings are accepted but do nothing; use rig_enabled, rig_url, and rig_token instead.

This is a clean service migration, not a screenshot-loop redesign. Kin still reads accessibility snapshots and targets semantic elements. The additions are on-demand page/display screenshots, tab and download handling, durable logins, an isolated remote shell, Rig memory, and a journaled human-control path for credentials.