Update tools/chelon-sign

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: atomicturtle

tools/chelon-sign

@@ -204,6 +204,9 @@ def gpg_mode(args: List[str]):
                         sys.exit(1)
                 sys.stdout.buffer.flush()
 
+    except ChelonClientError as e:
+        print(f"GPG Emulation Error (signing service): {e}", file=sys.stderr)
+        sys.exit(1)
     except Exception as e:
         print(f"GPG Emulation Error: {e}", file=sys.stderr)
         sys.exit(1)