fix: forzar LF en entrypoint.sh + environments postman + limpiar variables coleccion

- .gitattributes: añadir '*.sh text eol=lf' para evitar CRLF en Windows
- deployments/entrypoint.sh: renormalizado a LF
- postman_environments.json: entornos LOCAL/DEV/PROD en un único fichero
- postman_collection.json: eliminadas variables por defecto (vienen del entorno)

postman_collection.json

@@ -5,33 +5,7 @@
     "schema": "https://schema.getpostman.com/json/collection/v2.1.0/collection.json",
     "_postman_id": "django-core-base-collection"
   },
-  "variable": [
-    {
-      "key": "base_url",
-      "value": "http://localhost:8000",
-      "type": "string"
-    },
-    {
-      "key": "access_token",
-      "value": "",
-      "type": "string"
-    },
-    {
-      "key": "refresh_token",
-      "value": "",
-      "type": "string"
-    },
-    {
-      "key": "username",
-      "value": "admin",
-      "type": "string"
-    },
-    {
-      "key": "password",
-      "value": "admin",
-      "type": "string"
-    }
-  ],
+  "variable": [],
   "item": [
     {
       "name": "Auth",