Fix DataStar v1 RC8 signal attribute incompatibilities

Two bugs that caused signals to not work on the frontend:

1. data-on-signal-change → data-on-signal-patch
   The data-on-signal-change attribute was removed in RC8.
   The replacement is data-on-signal-patch.

2. data-bind-newTodo="" → data-bind="newTodo"
   HTML normalises attribute names to lowercase at parse time, so
   data-bind-newTodo becomes data-bind-newtodo in the DOM. DataStar
   would then bind to signal $newtodo instead of $newTodo, breaking
   the two-way binding. The value syntax data-bind="newTodo" preserves
   the camelCase name correctly.

https://claude.ai/code/session_01JThiQbp3Bn9J1VhBpRuz4u

examples/todo/todo_list.rs

@@ -40,13 +40,15 @@ pub async fn todo_list(cx: &mut RenderContext) -> anyhow::Result<Markup> {
             }
 
             // Add todo form.
-            // data-bind-newTodo binds the input to the $newTodo signal.
-            // The button uses new_todo.val ("$newTodo") in a DataStar expression.
+            // data-bind="newTodo" binds the input to the $newTodo signal.
+            // Value syntax is used instead of data-bind-newTodo because HTML
+            // normalises attribute names to lowercase, which would corrupt the
+            // camelCase signal name (newTodo → newtodo).
             div.add-form {
                 input
                     type="text"
                     placeholder="What needs to be done?"
-                    data-bind-newTodo=""
+                    data-bind="newTodo"
                     ;
                 button
                     data-on-click="@post('/action/add_todo')"