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/Add Ebook Folder.bru

@@ -0,0 +1,49 @@
+meta {
+  name: Add Ebook Folder
+  type: http
+  seq: 5
+}
+
+post {
+  url: {{base_url}}/api/auth/ebook-folders
+  body: json
+  auth: inherit
+}
+
+body {
+  {
+    "folder_path": "/path/to/ebooks"
+  }
+}
+
+settings {
+  encodeUrl: true
+  timeout: 0
+}
+
+docs {
+  ## Add Ebook Folder
+
+  Adds a new ebook folder for the authenticated user.
+
+  **Method:** POST
+
+  **Endpoint:** /api/auth/ebook-folders
+
+  **Authentication:** Required
+
+  **Request Body:**
+  - `folder_path` (string, required): Path to the ebook folder
+
+  **Response:**
+  - `id` (string): Folder ID
+  - `user_id` (string): User ID
+  - `folder_path` (string): Folder path
+  - `created_at` (string): Creation timestamp
+
+  **Status Codes:**
+  - 201: Created
+  - 400: Bad Request
+  - 401: Unauthorized
+  - 409: Conflict (folder already exists)
+}