feat: add dark mode, telemetry, and curl to Docker image

- Install `curl` in Dockerfile for healthcheck/tooling support
- Add class-based dark mode via Tailwind `@custom-variant` and a
  pre-paint `<script>` in `app.html` to avoid theme flash on load
- Implement theme toggle in layout with system preference detection,
  `localStorage` persistence, and smooth transitions
- Update all UI components with `dark:` variants for full dark mode
  support across backgrounds, borders, and text colours
- Add `sendTelemetry` helper in `api.ts` for fire-and-forget
  client-side error reporting to `/api/v1/telemetry`

docker-compose.yml

@@ -6,3 +6,9 @@ services:
     env_file:
       - .env
     restart: unless-stopped
+    healthcheck:
+      test: ["CMD-SHELL", "curl -f http://localhost:${NIKE_PORT:-8000}/live"]
+      interval: 30s
+      timeout: 10s
+      retries: 3
+      start_period: 40s