legacy UI (#4612)

# Description of Changes

<!--
Please provide a summary of the changes, including:

- What was changed
- Why the change was made
- Any challenges encountered

Closes #(issue_number)
-->

---

## Checklist

### General

- [ ] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [ ] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [ ] I have performed a self-review of my own code
- [ ] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [ ] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md#6-testing)
for more details.

---------

Co-authored-by: Claude <[email protected]>
Co-authored-by: EthanHealy01 <[email protected]>
Co-authored-by: EthanHealy01 <[email protected]>

frontend/src/services/preferencesService.ts

@@ -1,13 +1,16 @@
+import { ToolPanelMode } from 'src/contexts/toolWorkflow/toolWorkflowState';
 import { indexedDBManager, DATABASE_CONFIGS } from './indexedDBManager';
 
 export interface UserPreferences {
   autoUnzip: boolean;
   autoUnzipFileLimit: number;
+  defaultToolPanelMode: ToolPanelMode;
 }
 
 export const DEFAULT_PREFERENCES: UserPreferences = {
   autoUnzip: true,
   autoUnzipFileLimit: 4,
+  defaultToolPanelMode: 'sidebar',
 };
 
 class PreferencesService {