Stirling 2.0 (#3928)

# Description of Changes

<!--

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

-->

---

## 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/components/shared/NavigationWarningModal.tsx

@@ -0,0 +1,106 @@
+import React from 'react';
+import { Modal, Text, Button, Group, Stack } from '@mantine/core';
+import { useFileContext } from '../../contexts/FileContext';
+
+interface NavigationWarningModalProps {
+  onApplyAndContinue?: () => Promise<void>;
+  onExportAndContinue?: () => Promise<void>;
+}
+
+const NavigationWarningModal = ({
+  onApplyAndContinue,
+  onExportAndContinue
+}: NavigationWarningModalProps) => {
+  const { 
+    showNavigationWarning, 
+    hasUnsavedChanges,
+    confirmNavigation, 
+    cancelNavigation,
+    setHasUnsavedChanges
+  } = useFileContext();
+
+  const handleKeepWorking = () => {
+    cancelNavigation();
+  };
+
+  const handleDiscardChanges = () => {
+    setHasUnsavedChanges(false);
+    confirmNavigation();
+  };
+
+  const handleApplyAndContinue = async () => {
+    if (onApplyAndContinue) {
+      await onApplyAndContinue();
+    }
+    setHasUnsavedChanges(false);
+    confirmNavigation();
+  };
+
+  const handleExportAndContinue = async () => {
+    if (onExportAndContinue) {
+      await onExportAndContinue();
+    }
+    setHasUnsavedChanges(false);
+    confirmNavigation();
+  };
+
+  if (!hasUnsavedChanges) {
+    return null;
+  }
+
+  return (
+    <Modal
+      opened={showNavigationWarning}
+      onClose={handleKeepWorking}
+      title="Unsaved Changes"
+      centered
+      closeOnClickOutside={false}
+      closeOnEscape={false}
+    >
+      <Stack gap="md">
+        <Text>
+          You have unsaved changes to your PDF. What would you like to do?
+        </Text>
+        
+        <Group justify="flex-end" gap="sm">
+          <Button
+            variant="light"
+            color="gray"
+            onClick={handleKeepWorking}
+          >
+            Keep Working
+          </Button>
+          
+          <Button
+            variant="light"
+            color="red"
+            onClick={handleDiscardChanges}
+          >
+            Discard Changes
+          </Button>
+          
+          {onApplyAndContinue && (
+            <Button
+              variant="light"
+              color="blue"
+              onClick={handleApplyAndContinue}
+            >
+              Apply & Continue
+            </Button>
+          )}
+          
+          {onExportAndContinue && (
+            <Button
+              color="green"
+              onClick={handleExportAndContinue}
+            >
+              Export & Continue
+            </Button>
+          )}
+        </Group>
+      </Stack>
+    </Modal>
+  );
+};
+
+export default NavigationWarningModal;