fix(replace-and-invert-color): preserve original filename with '-inverted.pdf' suffix for output (#4594)

# Description of Changes

As the PR name suggests, replace-and-invert-color returned files _only_
named inverted.pdf instead of original name + inverted.pdf.


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- Why the change was made
- Any challenges encountered

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---

## 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)

### 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)

- [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 <bszucs1209@gmail.com>

app/core/src/main/java/stirling/software/SPDF/controller/api/misc/ReplaceAndInvertColorController.java

@@ -3,7 +3,6 @@ package stirling.software.SPDF.controller.api.misc;
 import java.io.IOException;
 
 import org.springframework.core.io.InputStreamResource;
-import org.springframework.http.HttpHeaders;
 import org.springframework.http.MediaType;
 import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.annotation.ModelAttribute;
@@ -18,6 +17,8 @@ import lombok.RequiredArgsConstructor;
 
 import stirling.software.SPDF.model.api.misc.ReplaceAndInvertColorRequest;
 import stirling.software.SPDF.service.misc.ReplaceAndInvertColorService;
+import stirling.software.common.util.GeneralUtils;
+import stirling.software.common.util.WebResponseUtils;
 
 @RestController
 @RequestMapping("/api/v1/misc")
@@ -33,7 +34,7 @@ public class ReplaceAndInvertColorController {
             description =
                     "This endpoint accepts a PDF file and provides options to invert all colors, replace"
                             + " text and background colors, or convert to CMYK color space for printing. Input:PDF Output:PDF Type:SISO")
-    public ResponseEntity<InputStreamResource> replaceAndInvertColor(
+    public ResponseEntity<byte[]> replaceAndInvertColor(
             @ModelAttribute ReplaceAndInvertColorRequest request) throws IOException {
 
         InputStreamResource resource =
@@ -45,9 +46,10 @@ public class ReplaceAndInvertColorController {
                         request.getTextColor());
 
         // Return the modified PDF as a downloadable file
-        return ResponseEntity.ok()
-                .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=inverted.pdf")
-                .contentType(MediaType.APPLICATION_PDF)
-                .body(resource);
+        String filename =
+                GeneralUtils.generateFilename(
+                        request.getFileInput().getOriginalFilename(), "_inverted.pdf");
+        return WebResponseUtils.bytesToWebResponse(
+                resource.getContentAsByteArray(), filename, MediaType.APPLICATION_PDF);
     }
 }