refactor: Reorganize Bruno requests by role permissions

- Create separate admin folder for admin-only operations
- Move admin endpoints (Create/Update/Delete Ebook, Scanner, Folder Management) to /bruno/admin/
- Add admin dashboard, profile, and library page requests
- Add Register Admin User request with explicit admin role
- Update Register User request to include role field
- Remove empty scanner folder structure

API organization:
- Admin requests: /bruno/admin/ (require admin role)
- User requests: /bruno/user/ (available to all authenticated users)
- Environment: Single {{token}} variable works for both roles

bruno/scanner/Scan Ebooks.bru

@@ -1,46 +0,0 @@
-meta {
-  name: Scan Ebooks
-  type: http
-  seq: 1
-}
-
-post {
-  url: {{base_url}}/api/scanner/scan
-  body: json
-  auth: inherit
-}
-
-settings {
-  encodeUrl: true
-  timeout: 0
-}
-
-docs {
-  ## Scan Ebooks
-  
-  Scans configured ebook folders for ebooks and adds them to the database. **Admin only operation.**
-  
-  **Method:** POST
-  
-  **Endpoint:** /api/scanner/scan
-  
-  **Authentication:** Required (Admin role required)
-  
-  **Request Body:**
-  - `folder_paths` (array of strings, optional): Array of folder paths to scan. If not provided, uses configured folders from Add Ebook Folder.
-  
-  **Response:**
-  - `message` (string): Success message
-  
-  **Status Codes:**
-  - 200: Success
-  - 400: Bad Request
-  - 401: Unauthorized
-  - 403: Forbidden (non-admin users)
-  
-  **Usage:**
-  - Without body: Scans all folders added via "Add Ebook Folder"
-  - With folder_paths: Scans the specified paths directly (useful for testing)
-  
-  **Note:** All discovered ebooks will be associated with the admin user who initiated the scan.
-}

bruno/scanner/Start Scanner.bru

@@ -1,39 +0,0 @@
-meta {
-  name: Start Scanner
-  type: http
-  seq: 2
-}
-
-post {
-  url: {{base_url}}/api/scanner/start
-  body: json
-  auth: inherit
-}
-
-settings {
-  encodeUrl: true
-  timeout: 0
-}
-
-docs {
-  ## Start Scanner
-  
-  Starts monitoring the specified folders for ebook changes.
-  
-  **Method:** POST
-  
-  **Endpoint:** /api/scanner/start
-  
-  **Authentication:** Required
-  
-  **Request Body:**
-  - `folder_paths` (array of strings, required): Array of folder paths to monitor
-  
-  **Response:**
-  - `message` (string): Success message
-  
-  **Status Codes:**
-  - 200: Success
-  - 400: Bad Request
-  - 401: Unauthorized
-}

bruno/scanner/Stop Scanner.bru

@@ -1,37 +0,0 @@
-meta {
-  name: Stop Scanner
-  type: http
-  seq: 3
-}
-
-post {
-  url: {{base_url}}/api/scanner/stop
-  body: none
-  auth: inherit
-}
-
-settings {
-  encodeUrl: true
-  timeout: 0
-}
-
-docs {
-  ## Stop Scanner
-
-  Stops monitoring folders for ebook changes.
-
-  **Method:** POST
-
-  **Endpoint:** /api/scanner/stop
-
-  **Authentication:** Required
-
-  **Request Body:** None
-
-  **Response:**
-  - `message` (string): Success message
-
-  **Status Codes:**
-  - 200: Success
-  - 401: Unauthorized
-}