fix: resolve gallery photo/thumbnail serving issues

- Change gallery photo URLs from static paths to API endpoints
- Add dedicated thumbnail serving endpoint for galleries
- Add test script to diagnose authentication issues
- Add nginx configuration documentation for Authorization header

This fixes the issue where photos and thumbnails work in admin but not
in gallery view. The problem was that static file routes with auth
middleware often have Authorization headers stripped by reverse proxies.
Using API endpoints ensures proper authentication handling.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/src/routes/gallery.js

@@ -136,8 +136,8 @@ router.get('/:slug/photos', verifyGalleryAccess, async (req, res) => {
       photos: photos.map(photo => ({
         id: photo.id,
         filename: photo.filename,
-        url: `/photos/${photo.path}`,
-        thumbnail_url: photo.thumbnail_path ? `/${photo.thumbnail_path}` : null,
+        url: `/api/gallery/${req.params.slug}/photo/${photo.id}`,
+        thumbnail_url: photo.thumbnail_path ? `/api/gallery/${req.params.slug}/thumbnail/${photo.id}` : null,
         type: photo.type,
         category_id: photo.category_id,
         category_name: photo.category_name,
@@ -320,6 +320,42 @@ router.get('/:slug/photo/:photoId', verifyGalleryAccess, async (req, res) => {
   }
 });
 
+// Serve thumbnail
+router.get('/:slug/thumbnail/:photoId', verifyGalleryAccess, async (req, res) => {
+  try {
+    const { photoId } = req.params;
+    
+    const photo = await db('photos')
+      .where({ id: photoId, event_id: req.event.id })
+      .first();
+    
+    if (!photo || !photo.thumbnail_path) {
+      return res.status(404).json({ error: 'Thumbnail not found' });
+    }
+    
+    const thumbPath = path.join(getStoragePath(), photo.thumbnail_path);
+    
+    // Check if file exists
+    const fs = require('fs').promises;
+    try {
+      await fs.access(thumbPath);
+    } catch (error) {
+      return res.status(404).json({ error: 'Thumbnail file not found' });
+    }
+    
+    // Set appropriate headers
+    res.setHeader('Content-Type', 'image/jpeg');
+    res.setHeader('Cache-Control', 'private, max-age=3600');
+    res.setHeader('Cross-Origin-Resource-Policy', 'cross-origin');
+    
+    // Send file
+    res.sendFile(path.resolve(thumbPath));
+  } catch (error) {
+    console.error('Error serving thumbnail:', error);
+    res.status(500).json({ error: 'Failed to serve thumbnail' });
+  }
+});
+
 // Get photo stats
 router.get('/:slug/stats', verifyGalleryAccess, async (req, res) => {
   try {