feat(nest-front): add API_URL proxy and VITE_API_URL support for split deployment

- nginx.conf: proxy /api/ to ${API_URL} (injected at container start via envsubst)
- Dockerfile: accept VITE_API_URL build arg; use envsubst CMD to hydrate nginx template
- src/utils/api.ts: export API_BASE using VITE_API_URL or fallback to /api

Enables nest-front to run on Coolify while nest-backend runs on Portainer.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

nest-front/Dockerfile

@@ -6,13 +6,25 @@ COPY package.json package-lock.json ./
 RUN npm ci
 
 COPY . .
+
+# VITE_API_URL is baked into the JS bundle at build time.
+# Default to /api so the nginx proxy is used when not overridden.
+ARG VITE_API_URL=/api
+ENV VITE_API_URL=$VITE_API_URL
+
 RUN npm run build
 
 FROM nginx:alpine
 
 COPY --from=build /app/dist /usr/share/nginx/html
-COPY nginx.conf /etc/nginx/conf.d/default.conf
+COPY nginx.conf /etc/nginx/nginx.conf.template
 
 EXPOSE 5173
 
-CMD ["nginx", "-g", "daemon off;"]
+# API_URL is the backend's public base URL used by nginx proxy_pass.
+# Set this at runtime in Coolify, e.g. API_URL=https://api.crowmate.fr
+ENV API_URL=http://localhost:3000
+
+# Substitute ${API_URL} in the nginx template at container start, then launch nginx.
+# The quoted variable list prevents envsubst from replacing nginx variables like $host.
+CMD ["/bin/sh", "-c", "envsubst '${API_URL}' < /etc/nginx/nginx.conf.template > /etc/nginx/conf.d/default.conf && nginx -g 'daemon off;'"]