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.

.github/scripts/check_language_properties.py

@@ -197,7 +197,7 @@ def check_for_differences(reference_file, file_list, branch, actor):
     if len(file_list) == 1:
         file_arr = file_list[0].split()
     base_dir = os.path.abspath(
-        os.path.join(os.getcwd(), "stirling-pdf", "src", "main", "resources")
+        os.path.join(os.getcwd(), "app", "core", "src", "main", "resources")
     )
 
     for file_path in file_arr:
@@ -219,13 +219,14 @@ def check_for_differences(reference_file, file_list, branch, actor):
                 # only local windows command
                 not file_normpath.startswith(
                     os.path.join(
-                        "", "stirling-pdf", "src", "main", "resources", "messages_"
+                        "", "app", "core", "src", "main", "resources", "messages_"
                     )
                 )
                 and not file_normpath.startswith(
                     os.path.join(
                         os.getcwd(),
-                        "stirling-pdf",
+                        "app",
+                        "core",
                         "src",
                         "main",
                         "resources",
@@ -328,7 +329,7 @@ def check_for_differences(reference_file, file_list, branch, actor):
         report.append("## ❌ Overall Check Status: **_Failed_**")
         report.append("")
         report.append(
-            f"@{actor} please check your translation if it conforms to the standard. Follow the format of [messages_en_GB.properties](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/stirling-pdf/src/main/resources/messages_en_GB.properties)"
+            f"@{actor} please check your translation if it conforms to the standard. Follow the format of [messages_en_GB.properties](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/app/core/src/main/resources/messages_en_GB.properties)"
         )
     else:
         report.append("## ✅ Overall Check Status: **_Success_**")
@@ -389,7 +390,8 @@ if __name__ == "__main__":
             file_list = glob.glob(
                 os.path.join(
                     os.getcwd(),
-                    "stirling-pdf",
+                    "app",
+                    "core",
                     "src",
                     "main",
                     "resources",