Fix INT: ContentSlider Slides editor wrote wrong prop key (image vs imageSrc)

MediaStylePanel's Slides array editor guarded on item.image !== undefined
and wrote `image` via AssetPicker's onChange, but ContentSlider (render
+ toHtml) reads slide.imageSrc. Default slides (imageSrc:'', no `image`
key) never showed an image picker at all, and any `image` value written
was a silent no-op on render/export.

Editor now guards/reads/writes `imageSrc` throughout, and the
"add slide" emptyItem matches defaultSlides' exact shape
(type/imageSrc/heading/text/bgColor).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

craft/src/components/sections/ContentSlider.toHtml.test.ts

@@ -91,3 +91,22 @@ describe('ContentSlider.toHtml autoplay silences aria-live and is pausable (F-ex
     expect(html).not.toMatch(/visibilitychange/);
   });
 });
+
+describe('ContentSlider.toHtml renders slide.imageSrc as a background-image (INT)', () => {
+  test('a slide with imageSrc set exports a background-image referencing it', () => {
+    const slidesWithImage = [
+      { type: 'image' as const, imageSrc: 'https://example.com/photo.jpg', heading: 'One' },
+    ];
+    const { html } = toHtml({ slides: slidesWithImage }, '');
+    expect(html).toContain("background-image:url('https://example.com/photo.jpg')");
+  });
+
+  test('a slide with no imageSrc falls back to bgColor (no broken/empty background-image url)', () => {
+    const slidesNoImage = [
+      { type: 'image' as const, imageSrc: '', heading: 'One', bgColor: '#123456' },
+    ];
+    const { html } = toHtml({ slides: slidesNoImage }, '');
+    expect(html).not.toContain('background-image:url(');
+    expect(html).toContain('background-color:#123456');
+  });
+});