feat(admin): external media import modal + thumbnail fixes for reference events\n\n- Photos tab: replace inline external folder picker with a modal opened via "Import from External Folder" button next to "Upload Photos"; add info that all pictures in the selected folder will be imported.\n- Admin thumbnails: align list endpoint to /api/admin/photos/:eventId/photos and always return thumbnail_url to trigger on-demand generation; normalize external paths to avoid duplicated folder segments (e.g., individual/individual) that broke resolver; improve thumbnail logging.\n- Use authenticated image fetching on admin feedback pages to prevent 401s in automation.\n- i18n: add backup.external.warning strings; complete German backup/restore coverage; add common keys (notSet, of, up, select, selected).\n- Docs: add Local (npm) setup for EXTERNAL_MEDIA_ROOT in deployment guide.\n\nRefs #17 – gallery feature request: https://github.com/the-luap/picpeak/issues/17

backend/src/services/imageProcessor.js

@@ -132,7 +132,8 @@ async function generateThumbnail(imagePath, options = {}) {
     
     return path.relative(getStoragePath(), thumbnailPath);
   } catch (error) {
-    logger.error(`Failed to generate thumbnail for ${filename}:`, error.message);
+    const msg = (error && error.message) ? error.message : String(error);
+    logger.error(`Failed to generate thumbnail for ${filename}: ${msg}`);
     
     // Clean up any partially created file
     try {
@@ -171,8 +172,18 @@ async function isThumbnailValid(thumbnailPath) {
  * Regenerate thumbnail if it's broken or missing
  */
 async function ensureThumbnail(photo) {
-  const storagePath = getStoragePath();
-  const originalPath = path.join(storagePath, 'events/active', photo.path);
+  const { db } = require('../database/db');
+  const { resolvePhotoFilePath } = require('./photoResolver');
+  let originalPath;
+  try {
+    const event = await db('events').where('id', photo.event_id).first();
+    originalPath = resolvePhotoFilePath(event, photo);
+    logger.info(`Ensuring thumbnail for photo ${photo.id} from source: ${originalPath}`);
+  } catch (e) {
+    const msg = (e && e.message) ? e.message : String(e);
+    logger.error(`Failed to resolve original path for thumbnail (photo ${photo.id}): ${msg}`);
+    return null;
+  }
   
   // Check if thumbnail exists and is valid
   if (photo.thumbnail_path) {