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

backend/.env.example

@@ -5,6 +5,7 @@ LOG_USE_UTC=false
 REQUEST_LOG_SLOW_MS=1000
 REQUEST_LOG_INCLUDE_HEALTH=false
 DATABASE_URL=postgresql+psycopg://postgres:postgres@localhost:5432/mission_control
+# For remote access, set this to your UI origin (e.g. http://<server-ip>:3000 or https://mc.example.com).
 CORS_ORIGINS=http://localhost:3000
 BASE_URL=
 # Security response headers (blank values disable each header).