feat: add BASE_PATH env var for serving UI from a subpath

When BASE_PATH is set (e.g., /server/), the entrypoint script injects
a <base> tag and rewrites asset paths in index.html. React Router reads
the basename from the <base> tag. Vite builds with relative paths.
Default / for standalone mode (no changes).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/Dockerfile

@@ -20,8 +20,15 @@ RUN npm run build
 FROM nginx:1.27-alpine
 COPY --from=build /app/dist /usr/share/nginx/html
 COPY nginx.conf /etc/nginx/templates/default.conf.template
+COPY docker-entrypoint.sh /cameleer-entrypoint.sh
+RUN chmod +x /cameleer-entrypoint.sh
 
 # Default API URL — override via K8s env or docker run -e
 ENV CAMELEER_API_URL=http://cameleer3-server:8081
+# Base path for serving the SPA from a subpath (e.g., /server/). Default: /
+ENV BASE_PATH=/
+
+ENTRYPOINT ["/cameleer-entrypoint.sh"]
+CMD ["nginx", "-g", "daemon off;"]
 
 EXPOSE 80