Add reinstate feature for deleted files

- Add MarkNotDeleted method to repository
- Add ReinstateFile method to service
- Add AdminReinstate handler
- Add /reinstate/:id route
- Add Reinstate button in admin menu for deleted files

internal/file/service.go

@@ -134,6 +134,29 @@ func (s *Service) ForceDelete(id string) (*FileRecord, error) {
 	return f, nil
 }
 
+func (s *Service) ReinstateFile(id string) (*FileRecord, error) {
+	f, err := s.repo.GetByID(id)
+	if err != nil {
+		return nil, err
+	}
+
+	if !f.Deleted {
+		return nil, ErrFileNotFound // or just return f, nil maybe?
+	}
+
+	// Check if file actually exists on disk
+	path := s.storageDir + "/" + f.ID
+	if _, err := os.Stat(path); os.IsNotExist(err) {
+		return nil, ErrFileNotFound
+	}
+
+	if err := s.repo.MarkNotDeleted(f); err != nil {
+		return nil, err
+	}
+
+	return f, nil
+}
+
 func (s *Service) GetPaginatedFiles(limit, offset int) ([]FileRecord, int, error) {
 	return s.repo.GetPaginated(limit, offset)
 }