A frame with borders tiles unless told to stretch

The fill of a sliced frame defaulted to `Stretch`. It is `Repeat` now, and the Fill dropdown lists
`Repeat` first.

The saved document keeps writing only the fill that differs from the default, so the key it
carries is now `stretch`, and a frame without it repeats. A frame saved before with the key
absent and meaning stretch would therefore tile; none of the stored projects has one - both sliced
frames on the server carry `fill: "repeat"` explicitly, so they draw as before.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/core/store/serialize.ts

@@ -33,7 +33,13 @@ import {
 import { PROJECT_FORMAT_VERSION, type Project } from '../model/Project';
 import { readScope } from '../model/Scope';
 import type { SceneObject } from '../model/SceneObject';
-import { isTextureFile, normalizeBorders, normalizeFrameRect, setFrameSlice } from '../model/texture';
+import {
+  DEFAULT_FILL,
+  isTextureFile,
+  normalizeBorders,
+  normalizeFrameRect,
+  setFrameSlice,
+} from '../model/texture';
 import { hasParentCycle } from '../model/walk';
 import {
   DECLARED_PORT_KINDS,
@@ -448,7 +454,7 @@ function normalizeTexture(
         rect.w,
         rect.h,
       ),
-      fill: f.fill === 'repeat' ? 'repeat' : 'stretch',
+      fill: f.fill === 'stretch' ? 'stretch' : DEFAULT_FILL,
     });
     frames.push(frame);
   }