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/workflows/check_properties.yml

@@ -4,7 +4,7 @@ on:
   pull_request_target:
     types: [opened, synchronize, reopened]
     paths:
-      - "stirling-pdf/src/main/resources/messages_*.properties"
+      - "app/core/src/main/resources/messages_*.properties"
 
 permissions:
   contents: read # Allow read access to repository content
@@ -67,7 +67,7 @@ jobs:
               exit 1
             fi
             # Get changed files and filter for properties files, handle case where no matches are found
-            gh pr view ${{ steps.get-pr-data.outputs.pr_number }} --json files -q ".files[].path" | grep -E '^stirling-pdf/src/main/resources/messages_[a-zA-Z_]{2}_[a-zA-Z_]{2,7}\.properties$' > changed_files.txt || echo "No matching properties files found in PR"
+            gh pr view ${{ steps.get-pr-data.outputs.pr_number }} --json files -q ".files[].path" | grep -E '^app/core/src/main/resources/messages_[a-zA-Z_]{2}_[a-zA-Z_]{2,7}\.properties$' > changed_files.txt || echo "No matching properties files found in PR"
             # Check if any files were found
             if [ ! -s changed_files.txt ]; then
               echo "No properties files changed in this PR"
@@ -117,7 +117,7 @@ jobs:
             const changedFiles = files
               .filter(file => 
                 file.status !== "removed" &&
-                /^stirling-pdf\/src\/main\/resources\/messages_[a-zA-Z_]{2}_[a-zA-Z_]{2,7}\.properties$/.test(file.filename)
+                /^app\/core\/src\/main\/resources\/messages_[a-zA-Z_]{2}_[a-zA-Z_]{2,7}\.properties$/.test(file.filename)
               )
               .map(file => file.filename);
 
@@ -157,12 +157,12 @@ jobs:
 
             // Determine reference file
             let referenceFilePath;
-            if (changedFiles.includes("stirling-pdf/src/main/resources/messages_en_GB.properties")) {
+            if (changedFiles.includes("app/core/src/main/resources/messages_en_GB.properties")) {
               console.log("Using PR branch reference file.");
               const { data: fileContent } = await github.rest.repos.getContent({
                 owner: prRepoOwner,
                 repo: prRepoName,
-                path: "stirling-pdf/src/main/resources/messages_en_GB.properties",
+                path: "app/core/src/main/resources/messages_en_GB.properties",
                 ref: branch,
               });
 
@@ -174,7 +174,7 @@ jobs:
               const { data: fileContent } = await github.rest.repos.getContent({
                 owner: repoOwner,
                 repo: repoName,
-                path: "stirling-pdf/src/main/resources/messages_en_GB.properties",
+                path: "app/core/src/main/resources/messages_en_GB.properties",
                 ref: "main",
               });