feat(test): extract anchor iPhone device descriptors to shared fixture

Move the four iPhone viewport descriptors (SE, 15/16, 16/17 Pro, Pro Max)
into tests/e2e/fixtures/devices.ts so the upcoming visual spec (Task 23)
can share the same anchors. The mobile-audit spec now spreads each
descriptor and adds a slug `name` plus a human `label` for the run header.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/e2e/fixtures/devices.ts

@@ -0,0 +1,44 @@
+/**
+ * Shared device descriptors for mobile/tablet Playwright runs.
+ *
+ * Anchors per docs/superpowers/specs/2026-04-29-mobile-optimization-design.md §2.1:
+ * narrowest, common, current Pro, current Pro Max.
+ */
+export const IPHONE_DEVICES = {
+  iphoneSe: {
+    name: 'iPhone SE 3 (375×667)',
+    viewport: { width: 375, height: 667 },
+    deviceScaleFactor: 2,
+    isMobile: true,
+    hasTouch: true,
+    userAgent:
+      'Mozilla/5.0 (iPhone; CPU iPhone OS 17_0 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/17.0 Mobile/15E148 Safari/604.1',
+  },
+  iphone16: {
+    name: 'iPhone 15/16 (393×852)',
+    viewport: { width: 393, height: 852 },
+    deviceScaleFactor: 3,
+    isMobile: true,
+    hasTouch: true,
+    userAgent:
+      'Mozilla/5.0 (iPhone; CPU iPhone OS 17_0 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/17.0 Mobile/15E148 Safari/604.1',
+  },
+  iphone16Pro: {
+    name: 'iPhone 16/17 Pro (402×874)',
+    viewport: { width: 402, height: 874 },
+    deviceScaleFactor: 3,
+    isMobile: true,
+    hasTouch: true,
+    userAgent:
+      'Mozilla/5.0 (iPhone; CPU iPhone OS 17_0 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/17.0 Mobile/15E148 Safari/604.1',
+  },
+  iphoneProMax: {
+    name: 'iPhone 16/17 Pro Max (440×956)',
+    viewport: { width: 440, height: 956 },
+    deviceScaleFactor: 3,
+    isMobile: true,
+    hasTouch: true,
+    userAgent:
+      'Mozilla/5.0 (iPhone; CPU iPhone OS 17_0 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/17.0 Mobile/15E148 Safari/604.1',
+  },
+} as const;