Make browser controls visible in chat and the Computer sidebar

[davidmckayv]

Computer access was hard to find: channel chat used an icon-only toggle, standalone Bot chat had no live sidebar, and takeover controls appeared only in the expanded viewer or a pending-help prompt.

Expose a labeled Computer toggle and state-aware Take control / Hand back controls in chat and in the computer sidebar. Reuse the existing request-aware ownership protocol and live viewer so every surface reflects the same control state, including loading and failures. Standalone Bot chat retains its selected Bot, history, and New chat behavior while gaining live computer access.

Validation:

• All 948 app tests passed, including shared ownership, concurrent actions/errors, historical screenshots, standalone draft/history/selection, and New chat regressions.
• App typecheck, scoped format/lint, and production build passed.
• The initial CI timeout in the new sidebar test was traced to large simulated-DOM error serialization. The close wait now checks node detachment; chat identity, draft, selected Bot, and New chat assertions remain. All 948 app tests passed again after this test-only correction.
• Actual localhost desktop UI: both chat routes open/close the live sidebar; takeover in chat and handback in the sidebar (and the reverse) update both surfaces. Drafts and selected Bot survive sidebar toggles; New chat still works.
• One scoped code review found no blocking issues. Earlier real Hacker News login/CAPTCHA handoff remains accepted: the user completed the challenge, handed back control, and the Bot confirmed the signed-in page.

Test limitation: a new simulated narrow-sheet close case triggered a Bun native SIGTRAP, so the standalone route regression uses explicit desktop geometry. Existing narrow DetailPanel tests and the full app suite pass. No mobile hands-on result is claimed.