Stream and control hosted macOS apps #2474

Track B of #2403. Contracts: contracts comment, sections 1 and 3.

Problem

People cannot see or control a hosted macOS app on a device-host Mac. Hosted viewing and input are hardcoded to iOS.

Evidence

• DeviceHost.viewTarget and bindView (packages/server/src/device-host.ts), HostedViews (packages/server/src/hosted-view.ts), and hostedMethod in packages/server/src/server.ts (subscribe passes platform: 'ios'; device-host.input.* covers touch, text, button, rotate and posture only).
• Local macOS viewing already works through FramePool and stim-frames macos <MacosAppState>. MacosSource.swift re-checks pid, start time, executable and bundle id every second and captures the single main window only. control.ts needs input.scroll and input.key for macOS.

Fix idea / scope

• Add readHostedMacosApp(home) to core/state: it reads the pseudo workspace record under a worker home without relying on the process's STIM_HOME.
• viewTarget accepts macOS sessions only while macosAppState(...).state === 'running'. HostedViews builds { platform: 'macos', app }. Its identity check compares launchId, pid and start time. A relaunch closes the view.
• Add device-host.input.scroll and device-host.input.key to the method lists, types and JSON Schema, routed like the other hosted inputs.
• TCC: the existing refusal text when Screen Recording or Accessibility is missing on the host. Never scripted.

Acceptance

• Server tests with a fake capture helper: a running hosted app can be subscribed (the helper gets macos plus the recorded JSON with the hosted bundle id) and controlled, including scroll and key. Viewing is refused before launch and after exit. Another client is refused. Existing iOS hosted tests stay unchanged and green.
• Real single-Mac check against track A's fixture flow: frames of the hosted fixture window come from the real stim-frames on this Mac (the capture host already has its grants), and a click reaches the fixture.

Out of scope

The client-side relay for Desktop and the phone (#2475).

Depends on #2473 (it can start on the A draft branch).