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/templates/partials/todo_row.heml

@@ -1,8 +1,12 @@
 <li +data-key="self.id">
   <span>{+ self.title +}</span>
-  <form data-hemx-handle="rename_todo">
+  <form data-hemx-handle="rename_todo" data-hemx-form="rename_todo">
     <input type="hidden" name="id" +value="self.id">
-    <button type="submit" name="title" value="Renamed todo">Rename</button>
+    <label>
+      Rename
+      <input name="title" +value="self.title" required="required">
+    </label>
+    <button type="submit">Save</button>
   </form>
   <form data-hemx-handle="delete_todo">
     <button type="submit" name="id" +value="self.id">Delete</button>