Stirling 2.0 (#3928)

# Description of Changes

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File context for managing files between tools and views
Optimisation for large files
Updated Split to work with new file system and match Matts stepped
design closer

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---

## 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: Anthony Stirling <[email protected]>

frontend/src/commands/pageCommands.ts

@@ -97,27 +97,8 @@ export class DeletePagesCommand extends PageCommand {
   }
 
   undo(): void {
-    let restoredPages = [...this.pdfDocument.pages];
-    
-    // Insert deleted pages back at their original positions
-    this.deletedPages
-      .sort((a, b) => (this.deletedPositions.get(a.id) || 0) - (this.deletedPositions.get(b.id) || 0))
-      .forEach(page => {
-        const originalIndex = this.deletedPositions.get(page.id) || 0;
-        restoredPages.splice(originalIndex, 0, page);
-      });
-    
-    // Update page numbers
-    restoredPages = restoredPages.map((page, index) => ({ 
-      ...page, 
-      pageNumber: index + 1 
-    }));
-    
-    this.setPdfDocument({ 
-      ...this.pdfDocument, 
-      pages: restoredPages, 
-      totalPages: restoredPages.length 
-    });
+    // Simply restore to the previous state (before deletion)
+    this.setPdfDocument(this.previousState);
   }
 
   get description(): string {