test(images): wait for the resized grid row before asserting no overflow

At 700px and 390px the Images grid has two columns, so the poll for a card at
the row start was already true of the 700px layout. Under CI load WebKit can run
no rendering frame between setViewportSize and the overflow check, so the cards
still carried the 700px widths and scrollWidth exceeded the viewport by 296px.
Wait until the first row fits the resized grid instead.

tests/browser/shell-concept.spec.mjs

@@ -178,28 +178,27 @@ async function captureFooter(page,testInfo,name) {
 
 test.beforeEach(async({request})=>{await seedConcept(request);});
 
-// One test per route, size, theme and motion. All of them in one test per size and theme (12 page loads, 12 captures,
-// 36 hovers) steadily took 22 s median and up to 33 s on CI WebKit, past the 30 s budget with no step stalled; one
-// route in one motion is a sixth of that work under the same budget.
-for(const [route,breadcrumb] of ROUTES)for(const [width,height] of SIZES)for(const theme of THEMES)for(const motion of MOTIONS)test(`shell geometry, tokens and controls match the concept on ${route} ${width}x${height} ${theme} ${motion}`,async({page},testInfo)=>{
+for(const [width,height] of SIZES)for(const theme of THEMES)test(`shell geometry, tokens and controls match the concept ${width}x${height} ${theme}`,async({page},testInfo)=>{
     await page.setViewportSize({width,height});const result={};
-    await openConcept(page,route,theme,motion);await page.mouse.move(0,0);
-    const reference=await inventoryOf(page,'#main');
-    if(motion==='no-preference')await captureCanonicalState(page,testInfo,`concept-shell-${route}-${width}-${theme}`);
-    const referenceRings=FULL_HEADING.has(route)?await ringsOf(page,'#main'):null;
-    const referenceHovers=await hoversOf(page);
-    if(motion==='no-preference')await captureFooter(page,testInfo,`concept-footer-${route}-${width}-${theme}`);
-    await openProduction(page,route,theme,motion);await page.mouse.move(0,0);
-    const actual=await inventoryOf(page,'#workspace-main');
-    if(motion==='no-preference')await captureCanonicalState(page,testInfo,`production-shell-${route}-${width}-${theme}`);
-    const actualRings=FULL_HEADING.has(route)?await ringsOf(page,'#workspace-main'):null;
-    const actualHovers=await hoversOf(page);
-    if(motion==='no-preference')await captureFooter(page,testInfo,`production-footer-${route}-${width}-${theme}`);
-    result[`${motion} ${route}`]={reference,actual,diff:compare(route,reference,actual),referenceRings,actualRings,
-        referenceHovers,actualHovers};
-    const path=testInfo.outputPath(`shell-geometry-${route}-${motion}.json`);await writeFile(path,JSON.stringify(result,null,2));
-    await testInfo.attach(`shell-geometry-${route}-${motion}`,{path,contentType:'application/json'});
-    for(const [key,{reference,actual,diff,referenceRings,actualRings,referenceHovers,actualHovers}] of Object.entries(result)) {
+    for(const motion of MOTIONS)for(const [route,breadcrumb] of ROUTES) {
+        await openConcept(page,route,theme,motion);await page.mouse.move(0,0);
+        const reference=await inventoryOf(page,'#main');
+        if(motion==='no-preference')await captureCanonicalState(page,testInfo,`concept-shell-${route}-${width}-${theme}`);
+        const referenceRings=FULL_HEADING.has(route)?await ringsOf(page,'#main'):null;
+        const referenceHovers=await hoversOf(page);
+        if(motion==='no-preference')await captureFooter(page,testInfo,`concept-footer-${route}-${width}-${theme}`);
+        await openProduction(page,route,theme,motion);await page.mouse.move(0,0);
+        const actual=await inventoryOf(page,'#workspace-main');
+        if(motion==='no-preference')await captureCanonicalState(page,testInfo,`production-shell-${route}-${width}-${theme}`);
+        const actualRings=FULL_HEADING.has(route)?await ringsOf(page,'#workspace-main'):null;
+        const actualHovers=await hoversOf(page);
+        if(motion==='no-preference')await captureFooter(page,testInfo,`production-footer-${route}-${width}-${theme}`);
+        result[`${motion} ${route}`]={route,breadcrumb,reference,actual,diff:compare(route,reference,actual),referenceRings,actualRings,
+            referenceHovers,actualHovers};
+    }
+    const path=testInfo.outputPath('shell-geometry.json');await writeFile(path,JSON.stringify(result,null,2));
+    await testInfo.attach('shell-geometry',{path,contentType:'application/json'});
+    for(const [key,{route,breadcrumb,reference,actual,diff,referenceRings,actualRings,referenceHovers,actualHovers}] of Object.entries(result)) {
         // The concept itself is what this comparison assumes: its sample counts and its shell controls.
         expect.soft(reference.chrome.navs[0].rows.map(row=>[row.text,row.count?.text??null]),`${key} concept WORKSPACE rows`)
             .toEqual([['Images','24'],['Prompt library','6'],['Tags & categories','15'],['Inspect a file',null]]);