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>

Dockerfile.ultra-lite

@@ -11,7 +11,11 @@ ENV DISABLE_ADDITIONAL_FEATURES=true \
     JAVA_CUSTOM_OPTS="" \
     PUID=1000 \
     PGID=1000 \
-    UMASK=022
+    UMASK=022 \
+    STIRLING_TEMPFILES_DIRECTORY=/tmp/stirling-pdf \
+    TMPDIR=/tmp/stirling-pdf \
+    TEMP=/tmp/stirling-pdf \
+    TMP=/tmp/stirling-pdf
 
 # Copy necessary files
 COPY scripts/download-security-jar.sh /scripts/download-security-jar.sh
@@ -35,10 +39,10 @@ RUN echo "@testing https://dl-cdn.alpinelinux.org/alpine/edge/main" | tee -a /et
         su-exec \
         openjdk21-jre && \
     # User permissions
-    mkdir -p /configs /logs /customFiles /usr/share/fonts/opentype/noto && \
+    mkdir -p /configs /logs /customFiles /usr/share/fonts/opentype/noto /tmp/stirling-pdf && \
     chmod +x /scripts/*.sh && \
     addgroup -S stirlingpdfgroup && adduser -S stirlingpdfuser -G stirlingpdfgroup && \
-    chown -R stirlingpdfuser:stirlingpdfgroup $HOME /scripts  /configs /customFiles /pipeline && \
+    chown -R stirlingpdfuser:stirlingpdfgroup $HOME /scripts  /configs /customFiles /pipeline /tmp/stirling-pdf && \
     chown stirlingpdfuser:stirlingpdfgroup /app.jar
 
 # Set environment variables
@@ -48,4 +52,4 @@ EXPOSE 8080/tcp
 
 # Run the application
 ENTRYPOINT ["tini", "--", "/scripts/init-without-ocr.sh"]
-CMD ["java", "-Dfile.encoding=UTF-8", "-jar", "/app.jar"]
+CMD ["java", "-Dfile.encoding=UTF-8", "-Djava.io.tmpdir=/tmp/stirling-pdf", "-jar", "/app.jar"]