refactor: rename bruno/auth folder to bruno/user

The auth folder now contains user management endpoints beyond just authentication:
- User registration/login (auth)
- Profile management (user)
- Theme settings (user preferences)
- Ebook folder management (user settings)

Renaming to 'user' better reflects the expanded scope covering user accounts, preferences, and settings management.

bruno/user/Login User.bru

@@ -0,0 +1,57 @@
+meta {
+  name: Login User
+  type: http
+  seq: 2
+}
+
+post {
+  url: {{base_url}}/api/auth/login
+  body: json
+  auth: inherit
+}
+
+body:json {
+  {
+    "login": "test@example.com",
+    "password": "password123"
+  }
+}
+
+script:post-response {
+  function onResponse(res) {
+    let data = res.getBody();
+    return bru.setEnvVar("token", data.token, { persist: true });
+  }
+  onResponse(res);
+}
+
+settings {
+  encodeUrl: true
+  timeout: 0
+}
+
+docs {
+  ## Login User
+  
+  Authenticates a user with email/username and password.
+  
+  **Method:** POST
+  
+  **Endpoint:** /api/auth/login
+  
+  **Request Body:**
+  - `login` (string): Email or username
+  - `password` (string): Password
+  
+  **Response:**
+  - `token` (string): JWT token
+  - `user` (object): User details
+    - `id` (string): User ID
+    - `email` (string): Email
+    - `username` (string): Username
+    - `theme` (string): User theme preference
+  
+  **Status Codes:**
+  - 200: Success
+  - 401: Invalid credentials
+}