Desktop shell: remote workspace — chat and read-only terminal

Problem

With visibility (#708 → #799) and control (#805) in place, a remote session still has no workspace in the desktop app: its transcript and terminal are only reachable in the web UI. This issue is delivery slice 3 (§9.3) of the spec at docs/superpowers/specs/2026-09-06-ai2371-desktop-remote-daemons-design.md (also posted on AI-2371). Blocked by #805, which ships the card host, the session authorization lifecycle, and the chat-pane decoupling this slice builds on.

Scope

Chat read path: seed from GET /api/sessions/{id}/detail, live-tail via hub SubscribeToStream (the Eventuous SignalR protocol — reference Eventuous.SignalR.Client rather than re-deriving it), rebuild turns client-side through an adapter feeding the existing chat item view models, resolve attribution via hub ResolveAttribution. The adapter is the natural first consumer of the canonical-transcript converters (Make Core the single home of transcript normalization #679) — build it as its own unit so those slot in. Queued input from SubscribeToChat + PendingInputChanged. Optional polish: SubscribeToAcpEphemeral live deltas (no client consumes them yet).
Chat write path: the composer sends hub SendUserInput(agentId, text, attachmentIds?) instead of PTY stdin.
Read-only terminal: SubscribeToTerminal (server replays its ring buffer), dimensions locked to the source, viewport reported via RequestResizeTerminal and released on close (never send the (0,0) sentinel), scrollback cleared before a re-subscribe replay, input limited to the fixed special-key set plus the composer.
Authorization signals for the transcript/terminal surfaces: the throwing surfaces are the oracle; the silently-denying terminal subscribe is attempted only after session access is established, so empty renders as "no output yet", distinct from loading and denied; watches and subscriptions re-establish per reconnect.
Origin-transition rebinding: an open workspace binds to the logical row, tears down and rebuilds origin-bound adapters on a Local↔Remote transition, never falsely ends a live session, and routes in-flight actions visibly.