Revert "Build post chat and attachment workflows"

This reverts commit 0b920da187.

backend/internal/calendar/attachments.go

@@ -137,26 +137,6 @@ func (s Store) FindAttachment(ctx context.Context, id string, viewerUserID strin
 	return scanAttachment(row)
 }
 
-func (s Store) DeleteAttachment(ctx context.Context, id string) (Attachment, error) {
-	row := s.db.QueryRow(ctx, `
-		DELETE FROM calendar_item_attachments
-		WHERE id = $1::uuid
-		RETURNING
-			id::text,
-			calendar_item_id::text,
-			original_filename,
-			stored_filename,
-			mime_type,
-			size_bytes,
-			storage_driver,
-			storage_path,
-			created_by::text,
-			created_at
-	`, id)
-
-	return scanAttachment(row)
-}
-
 type attachmentScanner interface {
 	Scan(dest ...any) error
 }