async _handleThumbnailCaching(id) {
        if (!id) return;
        
        const cachePath = path.join('./public/images', `${id}.png`);
        try {
            await fs.access(cachePath);
            console.log('[DEBUG] Thumbnail already cached');
        } catch (err) {
            console.log('Thumbnail not cached, fetching from Paperless');  
            const thumbnailData = await paperlessService.getThumbnailImage(id);
            if (!thumbnailData) {
                console.warn('Thumbnail nicht gefunden');
                return;
            }
            await fs.mkdir(path.dirname(cachePath), { recursive: true });
            await fs.writeFile(cachePath, thumbnailData);
        }
    }
Handle thumbnail caching for documents
@param {string} id - Document ID