test(shell): split the shell concept comparison per route and motion

"shell geometry, tokens and controls match the concept" compared all three
routes (Images, Library, Tags) under both motions in one test per size and
theme: 12 page loads, 12 captures and 36 hovers under the 30 s default
budget. Over the last 40 Viewer.js runs it took 22 s median and up to
33 s on CI WebKit, and timed out 6 times (main run 39886719087 among them).
The CI traces show steady progress with no stalled step (the longest one
is a 0.8 s navigation), so the cause is the amount of work in one test,
not a hang or a race.

Each route and motion is now its own test, still covering both sizes and
both themes, with the same assertions and captures.

Under run-pw-ci.sh on WebKit at 2 CPUs, --repeat-each=10:
before 18/40 timed out (median 26.9 s, max 32.5 s);
after 0/240 (median 6.5 s, p90 9.8 s, max 17.2 s).

tests/browser/shell-concept.spec.mjs

@@ -178,27 +178,28 @@ async function captureFooter(page,testInfo,name) {
 
 test.beforeEach(async({request})=>{await seedConcept(request);});
 
-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)=>{
+// 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} ${motion}`,async({page},testInfo)=>{
     await page.setViewportSize({width,height});const result={};
-    for(const motion of MOTIONS)for(const [route,breadcrumb] of ROUTES) {
-        await openConcept(page,route,theme,motion);await page.mouse.move(0,0);
-        const reference=await inventoryOf(page,'#main');
-        if(motion==='no-preference')await captureCanonicalState(page,testInfo,`concept-shell-${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} ${route}`]={route,breadcrumb,reference,actual,diff:compare(route,reference,actual),referenceRings,actualRings,
-            referenceHovers,actualHovers};
-    }
-    const path=testInfo.outputPath('shell-geometry.json');await writeFile(path,JSON.stringify(result,null,2));
-    await testInfo.attach('shell-geometry',{path,contentType:'application/json'});
-    for(const [key,{route,breadcrumb,reference,actual,diff,referenceRings,actualRings,referenceHovers,actualHovers}] of Object.entries(result)) {
+    await openConcept(page,route,theme,motion);await page.mouse.move(0,0);
+    const reference=await inventoryOf(page,'#main');
+    if(motion==='no-preference')await captureCanonicalState(page,testInfo,`concept-shell-${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}-${motion}`,{path,contentType:'application/json'});
+    for(const [key,{reference,actual,diff,referenceRings,actualRings,referenceHovers,actualHovers}] of Object.entries(result)) {
         // The concept itself is what this comparison assumes: its sample counts and its shell controls.
         expect.soft(reference.chrome.navs[0].rows.map(row=>[row.text,row.count?.text??null]),`${key} concept WORKSPACE rows`)
             .toEqual([['Images','24'],['Prompt library','6'],['Tags & categories','15'],['Inspect a file',null]]);