[V2] feat(attachments): add PDF/A-3b conversion, attachment listing, renaming, and deletion (#5304)

# Description of Changes

This pull request introduces major improvements to the PDF attachment
API, adding new endpoints for listing, renaming, and deleting
attachments in PDFs, as well as improving error handling and content
negotiation. It also adds support for converting PDFs to PDF/A-3b format
when adding attachments and introduces stricter validation for
attachment uploads. The exception handling is improved to ensure
consistent JSON error responses, even when the client requests a PDF.

**API Feature Additions:**

* Added new endpoints in `AttachmentController` for listing
(`/list-attachments`), renaming (`/rename-attachment`), and deleting
(`/delete-attachment`) PDF attachments, with corresponding request and
response models: `ListAttachmentsRequest`, `RenameAttachmentRequest`,
`DeleteAttachmentRequest`, and `AttachmentInfo`.

* Enhanced the `/add-attachments` endpoint to optionally convert the
resulting PDF to PDF/A-3b format, controlled by a new `convertToPdfA3b`
flag in `AddAttachmentRequest`.

**Validation and Robustness:**

* Introduced strict validation for attachment uploads, enforcing
non-empty attachments, a maximum size per attachment (50 MB), and a
total size limit (200 MB).

**Content Negotiation:**

* Updated `WebMvcConfig` to configure content negotiation, allowing both
PDF and JSON responses, and preventing 406 errors when clients request
PDFs but errors must be returned as JSON.


<img width="370" height="997" alt="image"
src="https://github.com/user-attachments/assets/571504d4-e97e-4b30-ae97-3defba217b47"
/>
<img width="1415" height="649" alt="image"
src="https://github.com/user-attachments/assets/bb8863fc-0be8-4bf2-af7d-73a229010f9a"
/>
<img width="1415" height="649" alt="image"
src="https://github.com/user-attachments/assets/68092672-5be5-4ef7-9cbc-1fb008b728e1"
/>
<img width="1415" height="649" alt="image"
src="https://github.com/user-attachments/assets/c4b0eda5-2573-4e38-8284-c077acb83f7f"
/>



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

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

Closes #(issue_number)
-->

---

## Checklist

### General

- [X] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [X] 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)
- [X] I have performed a self-review of my own code
- [X] 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)

### Translations (if applicable)

- [ ] I ran
[`scripts/counter_translation.py`](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/docs/counter_translation.md)

### UI Changes (if applicable)

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

### Testing (if applicable)

- [X] 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.

---------

Signed-off-by: Balázs Szücs <[email protected]>

frontend/src/core/hooks/tools/addAttachments/useAddAttachmentsOperation.ts

@@ -16,6 +16,8 @@ const buildFormData = (parameters: AddAttachmentsParameters, file: File): FormDa
     if (attachment) formData.append("attachments", attachment);
   });
 
+  formData.append("convertToPdfA3b", String(parameters.convertToPdfA3b));
+
   return formData;
 };
 

frontend/src/core/hooks/tools/addAttachments/useAddAttachmentsParameters.ts

@@ -2,10 +2,12 @@ import { useState } from 'react';
 
 export interface AddAttachmentsParameters {
   attachments: File[];
+  convertToPdfA3b: boolean;
 }
 
 const defaultParameters: AddAttachmentsParameters = {
-  attachments: []
+  attachments: [],
+  convertToPdfA3b: false
 };
 
 export const useAddAttachmentsParameters = () => {
@@ -33,3 +35,5 @@ export const useAddAttachmentsParameters = () => {
     validateParameters
   };
 };
+
+export const DEFAULT_ADD_ATTACHMENTS_PARAMETERS: AddAttachmentsParameters = defaultParameters;