feat(front): add sunbeam theme and Cunningham v4 token plumbing

Add sunbeam dark theme to cunningham.ts with amber brand palette and
navy grey scale. Wire THEME_CSS_URL through Dockerfile build args and
_app.tsx <link> injection so the integration service theme CSS loads at
runtime. Regenerate Cunningham design tokens (CSS, SCSS, TS). Add
Monaspace Neon variable font-face for monospace UI elements.

src/frontend/Dockerfile

@@ -41,9 +41,17 @@ FROM calendars AS calendars-builder
 WORKDIR /home/frontend/apps/calendars
 
 ARG API_ORIGIN
+ARG VISIO_BASE_URL
+ARG GAUFRE_WIDGET_PATH
+ARG GAUFRE_API_URL
+ARG THEME_CSS_URL
 ENV NEXT_PUBLIC_API_ORIGIN=${API_ORIGIN}
+ENV NEXT_PUBLIC_VISIO_BASE_URL=${VISIO_BASE_URL}
+ENV NEXT_PUBLIC_GAUFRE_WIDGET_PATH=${GAUFRE_WIDGET_PATH}
+ENV NEXT_PUBLIC_GAUFRE_API_URL=${GAUFRE_API_URL}
+ENV NEXT_PUBLIC_THEME_CSS_URL=${THEME_CSS_URL}
 
-RUN npm run build
+RUN npm run build-theme && npm run build
 
 # ---- Front-end image ----
 FROM caddy:2-alpine AS frontend-production