feat: UI animation enhancements across all major pages

P1 - Critical UX feedback:
- Add scale-in + slide-up-in entrance animations to profile popover and notification panel
- Port SmoothedProgressBar to EcommercePage (4 generation tools: clone, detail, tryOn, productSet)
- Add result-reveal stagger animation to ecommerce result grids
- Add heart-pop spring animation to CommunityPage favorite toggle

P2 - Visual polish:
- Add scroll-entrance IntersectionObserver animations for HomePage feature sections and experience section
- Add chat-message-in entrance animation to WorkbenchPage message rows
- Fix prefers-reduced-motion accessibility in WelcomeSplash canvas (skip animation, instant entry)

P3 - CSS consolidation:
- Remove conflicting .page-motion definition from legacy-pages.css (keep translateY version from legacy-components.css)
- Consolidate skeleton-shimmer: remove opacity-pulse keyframe from primitives.css, unify with gradient sweep
- Wire up --ease-spring token for heart-pop animation
- Add :active press states (scale 0.97) to topbar buttons, brand lockup

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

src/styles/pages/legacy-pages.css

@@ -14271,19 +14271,6 @@
 }
 
 /* ─── Page Motion Animation ─── */
-.page-motion {
-  animation: pixel-page-enter 0.3s ease-out;
-}
-
-@keyframes pixel-page-enter {
-  from {
-    opacity: 0;
-  }
-  to {
-    opacity: 1;
-  }
-}
-
 /* ─── Workbench Page Layout Overrides ─── */
 .ai-workbench-page.is-active .ai-workbench-shell {
   grid-template-columns: 1fr auto;
@@ -14865,6 +14852,8 @@
   display: flex;
   flex-direction: column;
   overflow: hidden;
+  animation: scale-in 150ms var(--ease-out-expo, cubic-bezier(0.16, 1, 0.3, 1)) both,
+             slide-up-in 150ms var(--ease-out-expo, cubic-bezier(0.16, 1, 0.3, 1)) both;
 }
 
 .notification-center__header {