dynamic port for UI from 8080 up (8081 etc) (#3042)

# Description of Changes

Please provide a summary of the changes, including:

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

Closes #(issue_number)

---

## 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/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)
- [ ] 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/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/utils/UrlUtils.java

@@ -1,5 +1,8 @@
 package stirling.software.SPDF.utils;
 
+import java.io.IOException;
+import java.net.ServerSocket;
+
 import jakarta.servlet.http.HttpServletRequest;
 
 public class UrlUtils {
@@ -14,4 +17,20 @@ public class UrlUtils {
 
         return scheme + "://" + serverName + ":" + serverPort + contextPath;
     }
+
+    public static boolean isPortAvailable(int port) {
+        try (ServerSocket socket = new ServerSocket(port)) {
+            return true;
+        } catch (IOException e) {
+            return false;
+        }
+    }
+
+    public static String findAvailablePort(int startPort) {
+        int port = startPort;
+        while (!isPortAvailable(port)) {
+            port++;
+        }
+        return String.valueOf(port);
+    }
 }