commit_message

feat: "Engine Room" UI redesign + Prometheus metrics endpoint

- Redesign chat.html with a distinctive industrial control-panel aesthetic:
  phosphor-green-on-charcoal dark theme (default), warm paper light theme
- New typography: IBM Plex Mono for UI chrome, labels, and user messages;
  Spectral serif for assistant prose replies
- LED status glow with breathe animation, blinking block cursor in status
  line, CRT scanline overlay (dark theme only), gradient temperature fader
- Restyle all modals, tabs, tables, alerts, badges, and history list with
  CSS variables so both themes are fully covered (replaces hardcoded dark
  modal overrides)
- Fix sidebar layout: .sidebar-full-content is now a flex column so section
  spacing and the actions' margin-top:auto actually apply
- Fix message entry animation so messages are never stuck invisible
  (removed opacity:0 default); copy button now appears on hover
- Move per-reply stats readout below the reply content instead of above
- Fix code blocks inside modal pres inheriting inline-code chip styling
- Style Firefox scrollbars (scrollbar-width/scrollbar-color)
- Add /metrics endpoint exposing Prometheus gauges for Ollama (up state,
  loaded model count, model size and VRAM per model)
- Add prometheus_client dependency to pyproject.toml and requirements.txt