V2 flatten (#4358)

# Description of Changes

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Please provide a summary of the changes, including:

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

Closes #(issue_number)
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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: James Brunton <jbrunton96@gmail.com>
Co-authored-by: ConnorYoh <40631091+ConnorYoh@users.noreply.github.com>

frontend/src/data/useTranslatedToolRegistry.tsx

@@ -15,6 +15,7 @@ import Repair from "../tools/Repair";
 import SingleLargePage from "../tools/SingleLargePage";
 import UnlockPdfForms from "../tools/UnlockPdfForms";
 import RemoveCertificateSign from "../tools/RemoveCertificateSign";
+import Flatten from "../tools/Flatten";
 import { compressOperationConfig } from "../hooks/tools/compress/useCompressOperation";
 import { splitOperationConfig } from "../hooks/tools/split/useSplitOperation";
 import { addPasswordOperationConfig } from "../hooks/tools/addPassword/useAddPasswordOperation";
@@ -28,6 +29,7 @@ import { ocrOperationConfig } from "../hooks/tools/ocr/useOCROperation";
 import { convertOperationConfig } from "../hooks/tools/convert/useConvertOperation";
 import { removeCertificateSignOperationConfig } from "../hooks/tools/removeCertificateSign/useRemoveCertificateSignOperation";
 import { changePermissionsOperationConfig } from "../hooks/tools/changePermissions/useChangePermissionsOperation";
+import { flattenOperationConfig } from "../hooks/tools/flatten/useFlattenOperation";
 import CompressSettings from "../components/tools/compress/CompressSettings";
 import SplitSettings from "../components/tools/split/SplitSettings";
 import AddPasswordSettings from "../components/tools/addPassword/AddPasswordSettings";
@@ -39,6 +41,7 @@ import AddWatermarkSingleStepSettings from "../components/tools/addWatermark/Add
 import OCRSettings from "../components/tools/ocr/OCRSettings";
 import ConvertSettings from "../components/tools/convert/ConvertSettings";
 import ChangePermissionsSettings from "../components/tools/changePermissions/ChangePermissionsSettings";
+import FlattenSettings from "../components/tools/flatten/FlattenSettings";
 import { ToolId } from "../types/toolId";
 
 const showPlaceholderTools = true; // Show all tools; grey out unavailable ones in UI
@@ -198,10 +201,14 @@ export function useFlatToolRegistry(): ToolRegistry {
       flatten: {
         icon: <LocalIcon icon="layers-clear-rounded" width="1.5rem" height="1.5rem" />,
         name: t("home.flatten.title", "Flatten"),
-        component: null,
+        component: Flatten,
         description: t("home.flatten.desc", "Remove all interactive elements and forms from a PDF"),
         categoryId: ToolCategoryId.STANDARD_TOOLS,
         subcategoryId: SubcategoryId.DOCUMENT_SECURITY,
+        maxFiles: -1,
+        endpoints: ["flatten"],
+        operationConfig: flattenOperationConfig,
+        settingsComponent: FlattenSettings,
       },
       "unlock-pdf-forms": {
         icon: <LocalIcon icon="preview-off-rounded" width="1.5rem" height="1.5rem" />,