test(bruno): add system settings API tests and update list users test

System Settings Bruno Tests (new):
- bruno/system/get-scan-settings.bru
- bruno/system/update-scan-settings.bru
- Test GET endpoint for retrieving system scan settings
- Test PUT endpoint for updating system scan settings
- Include admin authentication requirements
- Document response structures

List Users Bruno Test (update):
- bruno/user/admin/List Users.bru
- Add max_devices to response documentation
- Add device_count to response documentation
- Update feature descriptions

These Bruno tests provide API contract verification for the new
system settings endpoints and document the enhanced user list response.

bruno/system/update-scan-settings.bru

@@ -0,0 +1,36 @@
+meta {
+  name: Update System Scan Settings
+  type: http
+  seq: 2
+}
+
+put {
+  url: {{base_url}}/api/libraries/scan-settings
+  body: json
+  auth: inherit
+}
+
+headers {
+  Content-Type: application/json
+}
+
+body:json {
+  "scan_frequency_minutes": 30,
+  "auto_scan_enabled": true
+}
+
+script:post-response {
+  res.status.should.equal(200);
+  res.body.type.should.equal("application/json");
+  res.body.should.have.property('message');
+}
+
+docs {
+  ## Update System Scan Settings
+
+  Updates system-wide scan settings that apply to all libraries.
+
+  **Authentication**: Admin token required
+  **Request**: Scan frequency (15-1440 minutes) and enabled status
+  **Response**: Success message
+}