feat(mobile): compare table scroll fade and native share sheet

MOB-14: PerformanceChart and ComparisonChart both already configure
legend position 'top' — no change needed.

MOB-15: Compare's detailedTable is 774px wide inside an overflow-x:
auto wrapper. Add a right-edge mask-image fade at ≤640px so phone
users see the table extends past the viewport.

MOB-16: ComparisonView's Share button previously did clipboard-only.
Prefer navigator.share when available (iOS/Android native sheet) so
users can send straight to Messages / WhatsApp / Mail / etc. Fall
back to clipboard with the existing "Copied!" toast otherwise. User
cancellations swallow silently; only real errors trigger fallback.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

nextjs-app/components/ComparisonView.module.css

@@ -306,6 +306,15 @@
   -webkit-overflow-scrolling: touch;
 }
 
+/* Right-edge fade so phone users see the comparison table scrolls.
+   Otherwise the wider-than-viewport table silently clips. */
+@media (max-width: 640px) {
+  .tableWrapper {
+    -webkit-mask-image: linear-gradient(to right, #000 calc(100% - 28px), transparent);
+            mask-image: linear-gradient(to right, #000 calc(100% - 28px), transparent);
+  }
+}
+
 .comparisonTable {
   width: 100%;
   border-collapse: separate;