refactor(env): update NEXT_PUBLIC_API_URL to use 'auto' for better flexibility

frontend/Dockerfile

@@ -13,7 +13,7 @@ COPY --from=deps /app/node_modules ./node_modules
 COPY . ./
 
 # Allows configuring the API URL at build time.
-ARG NEXT_PUBLIC_API_URL=http://localhost:8000
+ARG NEXT_PUBLIC_API_URL=auto
 ENV NEXT_PUBLIC_API_URL=${NEXT_PUBLIC_API_URL}
 ARG NEXT_PUBLIC_AUTH_MODE
 ENV NEXT_PUBLIC_AUTH_MODE=${NEXT_PUBLIC_AUTH_MODE}
@@ -28,7 +28,7 @@ ARG NEXT_PUBLIC_AUTH_MODE
 
 # If provided at runtime, Next will expose NEXT_PUBLIC_* to the browser as well
 # (but note some values may be baked at build time).
-ENV NEXT_PUBLIC_API_URL=http://localhost:8000
+ENV NEXT_PUBLIC_API_URL=auto
 ENV NEXT_PUBLIC_AUTH_MODE=${NEXT_PUBLIC_AUTH_MODE}
 
 COPY --from=builder /app/.next ./.next