The reason recorded for CLI_NO_SUITABLE_OBJECTS (-50) assumed a 3mf being uploaded. The CLI also slices STL, OBJ and STEP input, so the reason now states what both -50 sites check: the plate is empty, or no object on it is both printable and fully inside the print volume. The exit code is unchanged.
Adds tests/cli/test_cli_no_suitable_objects.sh.
