Board + ticket detail web UI over the tracker API

[0xbeckett]

A React + Tailwind + shadcn single-page app over the existing tracker HTTP API, served by the
same server via a new static route + content negotiation. The JSON API surface is unchanged.

• Board — columns derived from the real TicketState enum, #N.x children nested under
  their parent, unmet needs rendered as a blocked affordance, cast/harness and staffed
  indicator on each card.
• Ticket detail — body, criteria, state + stateReason, needs, children, cast, plus the
  journal as the primary narrative and the raw event log as a secondary view.
• Actions — staff, nudge, pause, resume, gate (verdict + note), cancel; cancel confirms
  first, API errors surface as toasts.
• Live — board and open ticket poll on a short interval, paused while the tab is hidden.

Dark mode from tokens on day one; sourced from shadcn primitives and rethemed.

npm run build, npm run typecheck and npm test pass; a new test/server-ui.test.ts
covers the static route.