Feature/v2/pageeditor improved (#4289)

# Description of Changes

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

Rewrite of page editor to make it work properly.  
Added page breaks
Added merged file support
Added "insert file" support
Slight Ux improvements

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: Anthony Stirling <[email protected]>

frontend/src/contexts/file/fileActions.ts

@@ -84,6 +84,9 @@ interface AddFileOptions {
   
   // For 'stored' files
   filesWithMetadata?: Array<{ file: File; originalId: FileId; metadata: FileMetadata }>;
+  
+  // Insertion position
+  insertAfterPageId?: string;
 }
 
 /**
@@ -164,6 +167,11 @@ export async function addFiles(
           }
         }
         
+        // Store insertion position if provided
+        if (options.insertAfterPageId !== undefined) {
+          record.insertAfterPageId = options.insertAfterPageId;
+        }
+        
         // Create initial processedFile metadata with page count
         if (pageCount > 0) {
           record.processedFile = createProcessedFile(pageCount, thumbnail);
@@ -201,6 +209,11 @@ export async function addFiles(
           }
         }
         
+        // Store insertion position if provided
+        if (options.insertAfterPageId !== undefined) {
+          record.insertAfterPageId = options.insertAfterPageId;
+        }
+        
         // Create processedFile with provided metadata
         if (pageCount > 0) {
           record.processedFile = createProcessedFile(pageCount, thumbnail);
@@ -271,6 +284,11 @@ export async function addFiles(
           }
         }
         
+        // Store insertion position if provided
+        if (options.insertAfterPageId !== undefined) {
+          record.insertAfterPageId = options.insertAfterPageId;
+        }
+        
         // Create processedFile metadata with correct page count
         if (pageCount > 0) {
           record.processedFile = createProcessedFile(pageCount, metadata.thumbnail);