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/features/workbench/WorkbenchPage.tsx

@@ -2914,7 +2914,7 @@ function WorkbenchPage({
                         </div>
                       )}
                       {messages.map((message) => (
-                        <article key={message.id} className={`ai-chat-message-row${message.role === "user" ? " is-user" : ""}`}>
+                        <article key={message.id} className={`ai-chat-message-row chat-message-enter${message.role === "user" ? " is-user" : ""}`}>
                           <div className={`ai-chat-avatar${message.role === "user" ? " ai-chat-avatar--user" : ""}`}>
                             {message.role === "user" ? "我" : "AI"}
                           </div>