feat: rename import/export buttons to Import Story / Export Story

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/routes/Build.tsx

@@ -139,7 +139,7 @@ export function Editor({ story }: { story: Story }) {
             )
           }
         >
-          Export JSON
+          Export Story
         </button>
         {published && <Link to={`/play/${story.id}`}>Play →</Link>}
         <span role="status">{message ?? (dirty ? "Unsaved changes" : "")}</span>

src/routes/BuildList.tsx

@@ -49,7 +49,7 @@ export function BuildList() {
       <p>
         <button onClick={create}>New story</button>{" "}
         <label className="button">
-          Import JSON
+          Import Story
           <input
             type="file"
             accept="application/json,.json"