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/admin/Get Admin Dashboard.bru

@@ -0,0 +1,10 @@
+meta {
+  name: Get Admin Dashboard
+  type: http
+  seq: 10
+}
+
+get {
+  url: {{base_url}}/admin
+  auth: bearer
+}

bruno/admin/Get Admin Library.bru

@@ -0,0 +1,10 @@
+meta {
+  name: Get Admin Library
+  type: http
+  seq: 12
+}
+
+get {
+  url: {{base_url}}/admin/library
+  auth: bearer
+}

bruno/admin/Get Admin Profile.bru

@@ -0,0 +1,10 @@
+meta {
+  name: Get Admin Profile
+  type: http
+  seq: 11
+}
+
+get {
+  url: {{base_url}}/admin/profile
+  auth: bearer
+}