fix(pipeline): allow slashes in pipeline operation values (#4066)

# Description of Changes

- Extended the validation regex for `operation` in the pipeline
processor to allow slashes (`/`), in addition to alphanumeric
characters, underscores, and hyphens.
- This resolves the issue where valid operation strings (e.g., with
subpaths like `/api/v1/general/remove-pages`) were incorrectly rejected.
- Added an explicit log message for better debugging in case of invalid
`operation` values.

---

## 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)

- [ ] 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.

app/core/src/main/java/stirling/software/SPDF/controller/api/pipeline/PipelineProcessor.java

@@ -108,9 +108,13 @@ public class PipelineProcessor {
             if (inputFileTypes == null) {
                 inputFileTypes = new ArrayList<String>(Arrays.asList("ALL"));
             }
-            if (!operation.matches("^[a-zA-Z0-9_-]+$")) {
-                throw new IllegalArgumentException("Invalid operation value received.");
+
+            if (!apiDocService.isValidOperation(operation, parameters)) {
+                log.error("Invalid operation or parameters: o:{} p:{}", operation, parameters);
+                throw new IllegalArgumentException(
+                        "Invalid operation: " + operation + " with parameters: " + parameters);
             }
+
             String url = getBaseUrl() + operation;
             List<Resource> newOutputFiles = new ArrayList<>();
             if (!isMultiInputOperation) {
@@ -136,7 +140,7 @@ public class PipelineProcessor {
                             // skip
                             // this
                             // file
-                            if (operation.startsWith("filter-")
+                            if (operation.startsWith("/api/v1/filter/filter-")
                                     && (response.getBody() == null
                                             || response.getBody().length == 0)) {
                                 filtersApplied = true;