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/shell/app-shell.css

@@ -135,6 +135,11 @@
   font-size: 15px;
   font-weight: 900;
   cursor: pointer;
+  transition: opacity 160ms ease;
+}
+
+.brand-lockup:active {
+  opacity: 0.85;
 }
 
 .brand-lockup__mark {
@@ -303,6 +308,15 @@
   background: var(--bg-hover);
 }
 
+.creator-button:active,
+.member-button:active,
+.profile-button:active,
+.icon-button:active,
+.theme-toggle:active {
+  transform: scale(0.97);
+  transition-duration: 80ms;
+}
+
 .profile-button--guest:hover {
   background: rgba(var(--accent-rgb), 0.88);
   color: #07100b;