Add /review contract review shell

Builds a frontend-only Contract Review flow that reuses the existing
upload, document picker, and assistant chat plumbing - no new backend
routes.

- New route at /review with a 3-step lawyer-friendly UI:
    1. Choose contract (existing FileDirectory single-select +
       upload via uploadStandaloneDocument)
    2. Confirm review (selected doc, what Gary will look for,
       citation expectation, "answers are not legal advice")
    3. Review key terms (handed off to the assistant chat)
- Start Review builds a MikeMessage with a fixed review prompt and
  the chosen document, then reuses useAssistantChat.handleNewChat
  + router.push("/assistant/chat/{id}"), the same path used by
  the Gary-mode home InitialView. The new chat page auto-sends
  the prefilled message and streams the cited response.
- Updates the Gary-mode "Review Contract" card to point at /review
  instead of /tabular-reviews. /tabular-reviews is unchanged and
  still reachable from the sidebar.

No backend changes, no API contract changes, no auth/billing/teams,
no new providers. License unchanged.

https://claude.ai/code/session_019pRkhcGDRKQWHjzAnV5yCL