Multi module refactor (#3640)

# Description of Changes

Migrated Stirling PDF to a multi-module structure:

* Introduced new `:stirling-pdf` module
* Moved all the core logic and features of Stirling PDF into
`:stirling-pdf`
* Updated paths of jobs and scripts

---

## 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.

proprietary/src/test/java/stirling/software/proprietary/security/configuration/ee/LicenseKeyCheckerTest.java

@@ -0,0 +1,79 @@
+package stirling.software.proprietary.security.configuration.ee;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.verifyNoInteractions;
+import static org.mockito.Mockito.when;
+import static stirling.software.proprietary.security.configuration.ee.KeygenLicenseVerifier.License;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.junit.jupiter.api.io.TempDir;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import stirling.software.common.model.ApplicationProperties;
+
+@ExtendWith(MockitoExtension.class)
+class LicenseKeyCheckerTest {
+
+    @Mock private KeygenLicenseVerifier verifier;
+
+    @Test
+    void premiumDisabled_skipsVerification() {
+        ApplicationProperties props = new ApplicationProperties();
+        props.getPremium().setEnabled(false);
+        props.getPremium().setKey("dummy");
+
+        LicenseKeyChecker checker = new LicenseKeyChecker(verifier, props);
+
+        assertEquals(License.NORMAL, checker.getPremiumLicenseEnabledResult());
+        verifyNoInteractions(verifier);
+    }
+
+    @Test
+    void directKey_verified() {
+        ApplicationProperties props = new ApplicationProperties();
+        props.getPremium().setEnabled(true);
+        props.getPremium().setKey("abc");
+        when(verifier.verifyLicense("abc")).thenReturn(License.PRO);
+
+        LicenseKeyChecker checker = new LicenseKeyChecker(verifier, props);
+
+        assertEquals(License.PRO, checker.getPremiumLicenseEnabledResult());
+        verify(verifier).verifyLicense("abc");
+    }
+
+    @Test
+    void fileKey_verified(@TempDir Path temp) throws IOException {
+        Path file = temp.resolve("license.txt");
+        Files.writeString(file, "filekey");
+
+        ApplicationProperties props = new ApplicationProperties();
+        props.getPremium().setEnabled(true);
+        props.getPremium().setKey("file:" + file.toString());
+        when(verifier.verifyLicense("filekey")).thenReturn(License.ENTERPRISE);
+
+        LicenseKeyChecker checker = new LicenseKeyChecker(verifier, props);
+
+        assertEquals(License.ENTERPRISE, checker.getPremiumLicenseEnabledResult());
+        verify(verifier).verifyLicense("filekey");
+    }
+
+    @Test
+    void missingFile_resultsNormal(@TempDir Path temp) {
+        Path file = temp.resolve("missing.txt");
+        ApplicationProperties props = new ApplicationProperties();
+        props.getPremium().setEnabled(true);
+        props.getPremium().setKey("file:" + file.toString());
+
+        LicenseKeyChecker checker = new LicenseKeyChecker(verifier, props);
+
+        assertEquals(License.NORMAL, checker.getPremiumLicenseEnabledResult());
+        verifyNoInteractions(verifier);
+    }
+}