refactor: move modules under app/ directory and update file paths (#3938)

# Description of Changes

- **What was changed:**  
- Renamed top-level directories: `stirling-pdf` → `app/core`, `common` →
`app/common`, `proprietary` → `app/proprietary`.
- Updated all path references in `.gitattributes`, GitHub workflows
(`.github/workflows/*`), scripts (`.github/scripts/*`), `.gitignore`,
Dockerfiles, license files, and template settings to reflect the new
structure.
- Added a new CI job `check-generateOpenApiDocs` to generate and upload
OpenAPI documentation.
- Removed redundant `@Autowired` annotations from `TempFileShutdownHook`
and `UnlockPDFFormsController`.
- Minor formatting and comment adjustments in YAML templates and
resource files.

- **Why the change was made:**  
- To introduce a clear `app/` directory hierarchy for core, common, and
proprietary modules, improving organization and maintainability.
- To ensure continuous integration and Docker builds continue to work
seamlessly with the reorganized structure.
- To automate OpenAPI documentation generation as part of the CI
pipeline.

---

## Checklist

### General

- [x] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [x] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/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/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [x] I have performed a self-review of my own code
- [x] 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/devGuide/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/devGuide/DeveloperGuide.md#6-testing)
for more details.

Dockerfile.ultra-lite

@@ -22,7 +22,7 @@ COPY scripts/download-security-jar.sh /scripts/download-security-jar.sh
 COPY scripts/init-without-ocr.sh /scripts/init-without-ocr.sh
 COPY scripts/installFonts.sh /scripts/installFonts.sh
 COPY pipeline /pipeline
-COPY stirling-pdf/build/libs/*.jar app.jar
+COPY app/core/build/libs/*.jar app.jar
 
 # Set up necessary directories and permissions
 RUN echo "@testing https://dl-cdn.alpinelinux.org/alpine/edge/main" | tee -a /etc/apk/repositories && \
@@ -52,4 +52,4 @@ EXPOSE 8080/tcp
 
 # Run the application
 ENTRYPOINT ["tini", "--", "/scripts/init-without-ocr.sh"]
-CMD ["java", "-Dfile.encoding=UTF-8", "-Djava.io.tmpdir=/tmp/stirling-pdf", "-jar", "/app.jar"]
+CMD ["java", "-Dfile.encoding=UTF-8", "-Djava.io.tmpdir=/tmp/stirling-pdf", "-jar", "/app.jar"]