Auto-create one movement group when creating a new workout (#15)

Instead of starting with an empty groups array, new workouts now
include one movement group with a blank movement and a default set
(5 reps × 1 @ 0), so the editor is immediately ready for input.

https://claude.ai/code/session_01NcqwefXDNkEAmXJ6kou93E

Co-authored-by: Claude <noreply@anthropic.com>

Author: benmosher

src/WorkoutList.tsx

@@ -81,7 +81,16 @@ export default function WorkoutList() {
       <button
         type="button"
         onClick={async () => {
-          const id = await putWorkout({ name: "", groups: [] });
+          const id = await putWorkout({
+            name: "",
+            groups: [
+              {
+                movements: [
+                  { name: "", maxId: null, sets: [{ reps: 5, count: 1, weight: 0 }] },
+                ],
+              },
+            ],
+          });
           navigate(`/workouts/${id}/edit`);
         }}
       >