test(review): #90 assert Primary photo src is valid + checkerboard on strip

Locks in the two live-bug fixes: the Primary (leftmost kept) photo's <img src>
must be a real URL (blob: for an in-memory capture blob) and never empty/
"object Blob"; and each strip card must carry the gray checkerboard
background matching the Capture lineup.

frontend/tests/e2e/review-photo-strip.spec.ts

@@ -200,6 +200,18 @@ test.describe('M3 Review photo strip (#90)', () => {
     await expect(cards.nth(0)).toHaveAttribute('data-primary', 'true');
     await expect(page.getByText('PRIMARY', { exact: true })).toHaveCount(1);
 
+    // Bug #1 regression: the primary photo's <img src> must be a valid URL
+    // (blob: for an in-memory capture blob), never empty or "object Blob".
+    const primaryImg = cards.nth(0).locator('img');
+    await expect(primaryImg).not.toHaveAttribute('src', /object Blob|^$/);
+    const src = await primaryImg.getAttribute('src');
+    expect(src && src.length > 4).toBeTruthy();
+
+    // Bug #2 regression: the card carries the gray checkerboard background
+    // (matching the Capture lineup), not a flat color.
+    const bgImage = await cards.nth(0).evaluate((el) => getComputedStyle(el).backgroundImage);
+    expect(bgImage).toContain('45deg');
+
     // Remove the primary (cal) → primary auto-promotes to the next leftmost (ov).
     await cards.nth(0).click();
     await expect(cards.nth(0)).toHaveAttribute('aria-pressed', 'false');