model: rename a definition and every reference to it (model.rename, #290)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

crates/engine/src/cmd/mod.rs

@@ -131,6 +131,7 @@ pub static ALL: &[CommandSpec] = &[
     define::STEP_EDIT,
     define::STEP_DELETE,
     define::STEP_ACTIVATE,
+    define::RENAME,
     define::ACTIVITY,
     file::OPEN,
     file::SAVE,