feat: Implement blog and blog post models, routes, and services

- Added Blog and BlogPost models with necessary fields and relationships.
- Created blogRouter for handling blog-related API endpoints including CRUD operations.
- Developed BlogService for business logic related to blogs and posts, including sharing functionality.
- Implemented API client methods for frontend to interact with blog-related endpoints.
- Added internationalization support for blog-related text in English and German.
- Created Vue components for blog editing, listing, and viewing, including a rich text editor for post content.
- Enhanced user experience with form validations and dynamic visibility settings based on user input.

backend/services/socialnetworkService.js

@@ -467,6 +467,33 @@ class SocialNetworkService extends BaseService {
         return imagePath;
     }
 
+        // Public variant used by blog: allow access if the image's folder is visible to 'everyone'.
+        async getImageFilePathPublicByHash(hash) {
+            const image = await Image.findOne({ where: { hash } });
+            if (!image) {
+                throw new Error('Image not found');
+            }
+            const folder = await Folder.findOne({ where: { id: image.folderId } });
+            if (!folder) {
+                throw new Error('Folder not found');
+            }
+            const everyone = await ImageVisibilityType.findOne({ where: { description: 'everyone' } });
+            if (!everyone) {
+                throw new Error('Visibility type not found');
+            }
+            const hasEveryone = await FolderImageVisibility.findOne({ where: { folderId: folder.id, visibilityTypeId: everyone.id } });
+            if (!hasEveryone) {
+                const err = new Error('Access denied');
+                err.status = 403;
+                throw err;
+            }
+            const imagePath = this.buildFilePath(image.hash, 'user');
+            if (!fs.existsSync(imagePath)) {
+                throw new Error(`File "${imagePath}" not found`);
+            }
+            return imagePath;
+        }
+
     async checkUserImageAccess(userId, imageId) {
         const image = await Image.findByPk(imageId);
         if (image.userId === userId) {