feat:centralise temp-file management & cleanup across app/docker (#3797)

# Description of Changes
Introduces TempFileManager, registry, and scheduled cleanup service;
aligns all Docker images and runtime scripts to use a dedicated
/tmp/stirling-pdf directory; updates controllers, utilities, and tests
to use the new API; adds configurable system.tempFileManagement section.

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.

---------

Co-authored-by: a <a>

stirling-pdf/src/main/resources/application.properties

@@ -44,4 +44,7 @@ springdoc.swagger-ui.path=/index.html
 posthog.api.key=phc_fiR65u5j6qmXTYL56MNrLZSWqLaDW74OrZH0Insd2xq
 posthog.host=https://eu.i.posthog.com
 
-spring.main.allow-bean-definition-overriding=true
+spring.main.allow-bean-definition-overriding=true
+
+# Set up a consistent temporary directory location
+java.io.tmpdir=${stirling.tempfiles.directory:${java.io.tmpdir}/stirling-pdf}

stirling-pdf/src/main/resources/settings.yml.template

@@ -125,6 +125,15 @@ system:
       weasyprint: '' #Defaults to /opt/venv/bin/weasyprint
       unoconvert: '' #Defaults to /opt/venv/bin/unoconvert
   fileUploadLimit: '' # Defaults to "". No limit when string is empty. Set a number, between 0 and 999, followed by one of the following strings to set a limit. "KB", "MB", "GB".
+  tempFileManagement:
+    baseTmpDir: '' # Defaults to java.io.tmpdir/stirling-pdf
+    libreofficeDir: '' # Defaults to tempFileManagement.baseTmpDir/libreoffice  
+    systemTempDir: '' # Only used if cleanupSystemTemp is true
+    prefix: stirling-pdf- # Prefix for temp file names
+    maxAgeHours: 24 # Maximum age in hours before temp files are cleaned up
+    cleanupIntervalMinutes: 30 # How often to run cleanup (in minutes)
+    startupCleanup: true # Clean up old temp files on startup
+    cleanupSystemTemp: false # Whether to clean broader system temp directory
 
 ui:
   appName: '' # application's visible name