fix: multiple improvements and CI/CD updates

Frontend fixes:
- Add missing translations for chunk upload (upload.uploadingChunks, common.chunk)
- Fix photo deletion visual bug by tracking deletion state per photo
- Prevent UI confusion when deleting photos in admin grid

Backend fixes:
- Add file existence checks before deleting thumbnails
- Prevent ENOENT errors for missing thumbnail files
- Improve error handling in photo deletion

CI/CD updates:
- Remove Gitea release creation from Drone pipeline
- Simplify GitHub mirror workflow (remove history rewriting, keep file removal)
- Add clean-git-history.sh script for manual history cleanup

These changes improve the admin photo management experience and streamline
the CI/CD process for better maintainability.

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

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

frontend/src/components/admin/PhotoUpload.tsx

@@ -256,7 +256,7 @@ export const PhotoUpload: React.FC<PhotoUploadProps> = ({ eventId, onUploadCompl
           <div className="flex justify-between text-sm text-neutral-600 mb-1">
             <span>
               {t('upload.uploading')}
-              {totalChunks > 1 && ` (${t('common.chunk') || 'Chunk'} ${currentChunk}/${totalChunks})`}
+              {totalChunks > 1 && ` (${t('common.chunk')} ${currentChunk}/${totalChunks})`}
             </span>
             <span>{uploadProgress}%</span>
           </div>
@@ -268,7 +268,7 @@ export const PhotoUpload: React.FC<PhotoUploadProps> = ({ eventId, onUploadCompl
           </div>
           {totalChunks > 1 && (
             <p className="text-xs text-neutral-500 mt-1">
-              {t('upload.uploadingChunks') || `Uploading ${selectedFiles.length} files in ${totalChunks} batches...`}
+              {t('upload.uploadingChunks', { count: selectedFiles.length, total: totalChunks })}
             </p>
           )}
         </div>