feat(examples): make v0 todo rename form editable

Turn the v0 todo row rename action into an editable generated form instead of a fixed submit value, and preserve validation/recovery behavior for blank titles. This keeps the beginner exemplar on generated form handles and user-visible recovery instead of hidden demo shortcuts.

req: examples/001

req: canonical_authoring/003

examples/v0/src/main.rs

@@ -402,6 +402,13 @@ mod auth_handlers {
 
 fn rename_todo_effect(state: Arc<ExampleState>, form: RenameTodo) -> impl IntoEffect {
     // req: examples/001 req: canonical_authoring/003
+    if form.title.as_str().is_empty() {
+        return Some((
+            todo_row::rename_todo_form.focus("title"),
+            todos::notice.set("Add a title before renaming"),
+        ));
+    }
+
     let mut todos = state.todos.lock().unwrap();
     todos
         .iter_mut()
@@ -710,6 +717,20 @@ mod tests {
         assert!(add.payload_contains("Added Ship v0"));
         assert!(add.resets_form(todos::new_todo));
 
+        let rename_validation = inspect_batch(
+            InteractionRequest::from(form(
+                todo_row::rename_todo,
+                &[("id", "1"), ("title", "   ")],
+            ))
+            .dispatch_async(handlers(state.clone()))
+            .await
+            .unwrap()
+            .batch,
+        );
+        assert_eq!(state.todos.lock().unwrap()[0].title, "Ship v0");
+        assert!(rename_validation.payload_contains("Add a title before renaming"));
+        assert!(rename_validation.updates_text(todos::notice));
+
         let rename = inspect_batch(
             InteractionRequest::from(form(
                 todo_row::rename_todo,