Validate H2 datasource configuration in DatabaseService (#3449)

# Description of Changes

Please provide a summary of the changes, including:

- **What was changed**  
Updated the `isH2Database()` method in `DatabaseService.java` to perform
additional consistency checks between the configured datasource type and
the JDBC URL:
- Compute `isTypeH2` based on
`datasource.getType().equalsIgnoreCase("H2")`.
- Compute `isDBUrlH2` by checking if `datasource.getCustomDatabaseUrl()`
contains “h2” (case-insensitive).
- Log a warning and throw `IllegalStateException` when the type is H2
but URL doesn’t contain “h2”, or vice versa.
- Return the original boolean logic (`!enableCustomDatabase || isH2`)
only when both type and URL agree.

- **Why the change was made**  
To prevent runtime misconfigurations where the declared database driver
(H2) does not match the actual JDBC URL (or vice versa), providing
early, clear feedback to users and avoiding obscure errors later in
startup.


Closes #3428

---

## 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.

Co-authored-by: Anthony Stirling <77850077+Frooodle@users.noreply.github.com>

src/main/java/stirling/software/SPDF/config/security/database/DatabaseService.java

@@ -240,8 +240,32 @@ public class DatabaseService implements DatabaseInterface {
     private boolean isH2Database() {
         ApplicationProperties.Datasource datasource =
                 applicationProperties.getSystem().getDatasource();
-        return !datasource.isEnableCustomDatabase()
-                || datasource.getType().equalsIgnoreCase(ApplicationProperties.Driver.H2.name());
+
+        boolean isTypeH2 =
+                datasource.getType().equalsIgnoreCase(ApplicationProperties.Driver.H2.name());
+        boolean isDBUrlH2 =
+                datasource.getCustomDatabaseUrl().contains("h2")
+                        || datasource.getCustomDatabaseUrl().contains("H2");
+
+        if (isTypeH2 && !isDBUrlH2) {
+            log.warn(
+                    "Datasource type is H2, but the URL does not contain 'h2'. "
+                            + "Please check your configuration.");
+            throw new IllegalStateException(
+                    "Datasource type is H2, but the URL does not contain 'h2'. Please check your"
+                            + " configuration.");
+        } else if (!isTypeH2 && isDBUrlH2) {
+            log.warn(
+                    "Datasource URL contains 'h2', but the type is not H2. "
+                            + "Please check your configuration.");
+            throw new IllegalStateException(
+                    "Datasource URL contains 'h2', but the type is not H2. Please check your"
+                            + " configuration.");
+        }
+
+        boolean isH2 = isTypeH2 && isDBUrlH2;
+
+        return !datasource.isEnableCustomDatabase() || isH2;
     }
 
     /**