docs/mcp.md said that for both learn.markStep and learn.resetProgress a
missing, non-string or unknown `tutorial` is an error. learn.resetProgress
takes no params and clears the progress without reading `tutorial`
(crates/ui-egui/src/panels/learn.rs), so the sentence now names the
tutorial errors under learn.markStep alone, and the rule that an error
changes nothing stays with them.