Improve Type Safety and OpenAPI Schema for PDF API Controllers and Models (#3470)

# Description of Changes

- **What was changed**  
- Updated controller methods to use strongly‐typed primitives (`int`,
`long`, `boolean`) instead of `String` for numeric and boolean
parameters, eliminating calls to `Integer.parseInt`/`Long.parseLong` and
improving null‐safety (`Boolean.TRUE.equals(...)`).
- Enhanced all API request model classes with richer Swagger/OpenAPI
annotations: added `requiredMode`, `defaultValue`, `allowableValues`,
`format`, `pattern`, and tightened schema descriptions for all fields.
- Refactored HTML form templates for “Remove Blank Pages” to include
`min`, `max`, and `step` attributes on numeric inputs, matching the
updated validation rules.

- **Why the change was made**  
- **Type safety & robustness**: Shifting from `String` to native types
prevents runtime parsing errors, simplifies controller logic, and makes
default values explicit.
- **Better API documentation & validation**: Enriching the Swagger
annotations ensures generated docs accurately reflect required fields,
default values, and permitted ranges, which improves client code
generation and developer experience.
- **Consistency across codebase**: Aligning all request models and
controllers enforces a uniform coding style and reduces bugs.

#3406

---

## 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/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/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/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/DeveloperGuide.md#6-testing)
for more details.

src/main/java/stirling/software/SPDF/controller/api/CropController.java

@@ -39,8 +39,8 @@ public class CropController {
             description =
                     "This operation takes an input PDF file and crops it according to the given"
                             + " coordinates. Input:PDF Output:PDF Type:SISO")
-    public ResponseEntity<byte[]> cropPdf(@ModelAttribute CropPdfForm form) throws IOException {
-        PDDocument sourceDocument = pdfDocumentFactory.load(form);
+    public ResponseEntity<byte[]> cropPdf(@ModelAttribute CropPdfForm request) throws IOException {
+        PDDocument sourceDocument = pdfDocumentFactory.load(request);
 
         PDDocument newDocument =
                 pdfDocumentFactory.createNewDocumentBasedOnOldDocument(sourceDocument);
@@ -64,7 +64,8 @@ public class CropController {
             contentStream.saveGraphicsState();
 
             // Define the crop area
-            contentStream.addRect(form.getX(), form.getY(), form.getWidth(), form.getHeight());
+            contentStream.addRect(
+                    request.getX(), request.getY(), request.getWidth(), request.getHeight());
             contentStream.clip();
 
             // Draw the entire formXObject
@@ -76,7 +77,11 @@ public class CropController {
 
             // Now, set the new page's media box to the cropped size
             newPage.setMediaBox(
-                    new PDRectangle(form.getX(), form.getY(), form.getWidth(), form.getHeight()));
+                    new PDRectangle(
+                            request.getX(),
+                            request.getY(),
+                            request.getWidth(),
+                            request.getHeight()));
         }
 
         ByteArrayOutputStream baos = new ByteArrayOutputStream();
@@ -87,7 +92,7 @@ public class CropController {
         byte[] pdfContent = baos.toByteArray();
         return WebResponseUtils.bytesToWebResponse(
                 pdfContent,
-                form.getFileInput().getOriginalFilename().replaceFirst("[.][^.]+$", "")
+                request.getFileInput().getOriginalFilename().replaceFirst("[.][^.]+$", "")
                         + "_cropped.pdf");
     }
 }