[Golden-Pigeon]

Fixes #22.

Original problem

An approval for a mirrored remote Session could be answered automatically with unavailable when the local mirror runtime was not ready: the approval stream starts before the first session sync, so the user never saw the prompt and the remote turn could appear stuck. The approval was also dispatched as soon as the runtime mounted, before a client could present it.

Change

• Keep mirrored approvals queued until the mirror runtime exists and a connected client reports the local mirrored Session visible.
• The client's existing session-claim poll now also reports the currently visible local Session; the host uses a short freshness window.
• Dispatch queued approvals once through the ordinary native approval UI. Replayed approval ids are deduplicated.
• Add fake-host approval support and a two-client Playwright test.

Fixed during this change

• None.

Resolved

• An approval arriving before the mirror is ready is no longer answered unavailable on the user's behalf.
• An approval reaches the native approval UI only while a client is actually showing the mirrored Session.
• Two clients see one pending approval; when one answers, the other dismisses through the native approval cancel path, and the remote agent receives exactly one answer.

Unresolved

• The visibility signal reports the client's current Session; a mirrored Session open only in a background view is treated as not visible, and the approval waits until it is shown.
• No full SSH / real remote DSH E2E was run for this path; the end-to-end test uses an isolated DSH host with a fake remote agent.

Testing

• pnpm --filter dsh-remote-local-plugin test (129/129)
• pnpm --filter dsh-remote-local-plugin typecheck
• pnpm --filter @dsh-remote/testkit typecheck
• Full Playwright suite: 13/13, including the new two-client approval test: the approval arrives before any client shows the mirror; both clients see it; one answers; the other dismisses; the remote agent receives one allowed-once.