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

.env.example

@@ -12,6 +12,7 @@ POSTGRES_PASSWORD=postgres
 POSTGRES_PORT=5432
 
 # --- backend settings (see backend/.env.example for full list) ---
+# 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
 DB_AUTO_MIGRATE=true
 LOG_LEVEL=INFO
@@ -22,6 +23,6 @@ LOCAL_AUTH_TOKEN=
 
 # --- frontend settings ---
 # REQUIRED: Public URL used by the browser to reach the API.
-# If this is missing/blank, frontend API calls (e.g. Activity feed) will break.
-# Example (local dev / compose on your machine):
-NEXT_PUBLIC_API_URL=http://localhost:8000
+# Use `auto` to target the same host currently serving Mission Control on port 8000.
+# Example (explicit override): NEXT_PUBLIC_API_URL=https://mc.example.com
+NEXT_PUBLIC_API_URL=auto