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.dev

@@ -27,7 +27,11 @@ RUN apt-get update && apt-get install -y \
   && apt-get clean && rm -rf /var/lib/apt/lists/*
 
 # Setze die Environment Variable für setuptools
-ENV SETUPTOOLS_USE_DISTUTILS=local
+ENV SETUPTOOLS_USE_DISTUTILS=local \
+    STIRLING_TEMPFILES_DIRECTORY=/tmp/stirling-pdf \
+    TMPDIR=/tmp/stirling-pdf \
+    TEMP=/tmp/stirling-pdf \
+    TMP=/tmp/stirling-pdf
 
 # Installation der benötigten Python-Pakete
 RUN python3 -m venv --system-site-packages /opt/venv \
@@ -40,8 +44,9 @@ ENV PATH="/opt/venv/bin:$PATH"
 
 COPY . /workspace
 
-RUN adduser --disabled-password --gecos '' devuser \
-  && chown -R devuser:devuser /home/devuser /workspace
+RUN mkdir -p /tmp/stirling-pdf \
+  && adduser --disabled-password --gecos '' devuser \
+  && chown -R devuser:devuser /home/devuser /workspace /tmp/stirling-pdf
 RUN echo "devuser ALL=(ALL) NOPASSWD:ALL" > /etc/sudoers.d/devuser \
   && chmod 0440 /etc/sudoers.d/devuser