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`

docs/red_panda_standards.md

@@ -235,8 +235,6 @@ Place documentation in the `/docs/` directory of the repository.
 
 HTML documents must follow [docs/documentation_style_guide.html](documentation_style_guide.html).
 
-- Use Bootstrap CDN with Bootswatch theme **Flatly**
-- Include a dark mode toggle button in the navbar
-- Use Bootstrap Icons for icons
-- Use Bootstrap CSS for styles — avoid custom CSS
+- Include a dark mode that follows the system automatically and include a toggle button in the navbar
+- avoid custom CSS
 - Use **Mermaid** for diagrams