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.

app/core/.gitignore

@@ -0,0 +1,196 @@
+### Eclipse ###
+.metadata
+bin/
+tmp/
+*.tmp
+*.bak
+*.exe
+*.swp
+*~.nib
+local.properties
+.settings/
+.loadpath
+.recommenders
+.classpath
+.project
+version.properties
+
+#### Stirling-PDF Files ###
+pipeline/watchedFolders/
+pipeline/finishedFolders/
+customFiles/
+configs/
+watchedFolders/
+clientWebUI/
+!cucumber/
+!cucumber/exampleFiles/
+!cucumber/exampleFiles/example_html.zip
+exampleYmlFiles/stirling/
+/testing/file_snapshots
+SwaggerDoc.json
+
+# Gradle
+.gradle
+.lock
+
+# External tool builders
+.externalToolBuilders/
+
+# Locally stored "Eclipse launch configurations"
+*.launch
+
+# PyDev specific (Python IDE for Eclipse)
+*.pydevproject
+
+# CDT-specific (C/C++ Development Tooling)
+.cproject
+
+# CDT- autotools
+.autotools
+
+# Java annotation processor (APT)
+.factorypath
+
+# PDT-specific (PHP Development Tools)
+.buildpath
+
+# sbteclipse plugin
+.target
+
+# Tern plugin
+.tern-project
+
+# TeXlipse plugin
+.texlipse
+
+# STS (Spring Tool Suite)
+.springBeans
+
+# Code Recommenders
+.recommenders/
+
+# Annotation Processing
+.apt_generated/
+.apt_generated_test/
+
+# Scala IDE specific (Scala & Java development for Eclipse)
+.cache-main
+.scala_dependencies
+.worksheet
+
+# Uncomment this line if you wish to ignore the project description file.
+# Typically, this file would be tracked if it contains build/dependency configurations:
+#.project
+
+### Eclipse Patch ###
+# Spring Boot Tooling
+.sts4-cache/
+
+### Git ###
+# Created by git for backups. To disable backups in Git:
+# $ git config --global mergetool.keepBackup false
+*.orig
+
+# Created by git when using merge tools for conflicts
+*.BACKUP.*
+*.BASE.*
+*.LOCAL.*
+*.REMOTE.*
+*_BACKUP_*.txt
+*_BASE_*.txt
+*_LOCAL_*.txt
+*_REMOTE_*.txt
+
+### Java ###
+# Compiled class file
+*.class
+
+# Log file
+*.log
+
+# BlueJ files
+*.ctxt
+
+# Mobile Tools for Java (J2ME)
+.mtj.tmp/
+
+# Package Files #
+*.jar
+*.war
+*.nar
+*.ear
+*.zip
+*.tar.gz
+*.rar
+*.db
+/build/*
+/app/core/build/*
+
+# Byte-compiled / optimized / DLL files
+__pycache__/
+*.py[cod]
+*.pyo
+
+# Virtual environments
+.env*
+.venv*
+env*/
+venv*/
+ENV/
+env.bak/
+venv.bak/
+
+# VS Code
+/.vscode/**/*
+!/.vscode/settings.json
+!/.vscode/extensions.json
+
+# IntelliJ IDEA
+.idea/
+*.iml
+out/
+
+# Ignore Mac DS_Store files
+.DS_Store
+**/.DS_Store
+
+# cucumber
+/cucumber/reports/**
+
+# Certs and Security Files
+*.p12
+*.pk8
+*.pem
+*.crt
+*.cer
+*.cert
+*.der
+*.key
+*.csr
+*.kdbx
+*.jks
+*.asc
+
+# SSH Keys
+*.pub
+*.priv
+id_rsa
+id_rsa.pub
+id_ecdsa
+id_ecdsa.pub
+id_ed25519
+id_ed25519.pub
+.ssh/
+*ssh
+
+# cache
+.cache
+.ruff_cache
+.mypy_cache
+.pytest_cache
+.ipynb_checkpoints
+
+**/jcef-bundle/
+
+# node_modules
+node_modules/