refactor(animations): converge P1 motion durations to ≤300ms target

- 151 scripted + 1 manual duration fixes across 46 files
- framer entrance 0.5/0.6s -> 0.3s
- Tailwind hover -> duration-150, entrance -> duration-300
- preserve flip-clock/page-transition per semantic decision
- design-system.ts dead-code deferred
- P1 violations 156 -> 5; P0 remains 0; OK class 249 -> 400
- verified: tsc clean, eslint 0 errors
- verified: 130/130 jest suites, 1573 passed
- verified: visual regression 46/46 zero-pixel diff

Co-Authored-By: 阿睿 <workbuddy@tencent.com>

src/app/(marketing)/cases/cases-content-v3.tsx

@@ -25,10 +25,10 @@ function CaseCard({ caseItem, index }: { caseItem: CaseStudy; index: number }) {
       initial={{ opacity: 0, y: 20 }}
       whileInView={{ opacity: 1, y: 0 }}
       viewport={{ once: true, margin: '-60px' }}
-      transition={{ duration: 0.6, delay: index * 0.06, ease: EASE_OUT }}
-      className="group relative block overflow-hidden border border-border-primary hover:border-border-secondary bg-white hover:bg-bg-secondary transition-all duration-500 flex flex-col h-full"
+      transition={{ duration: 0.3, delay: index * 0.06, ease: EASE_OUT }}
+      className="group relative block overflow-hidden border border-border-primary hover:border-border-secondary bg-white hover:bg-bg-secondary transition-all duration-150 flex flex-col h-full"
     >
-      <div className="absolute top-0 left-0 h-0 w-[2px] group-hover:h-full transition-all duration-500 origin-top bg-brand" />
+      <div className="absolute top-0 left-0 h-0 w-[2px] group-hover:h-full transition-all duration-150 origin-top bg-brand" />
 
       <div className="p-6 sm:p-7 lg:p-8 flex flex-col flex-1 relative z-10">
         <div className="flex items-center gap-3 mb-5">
@@ -207,7 +207,7 @@ export default function CasesContentV3({
                 initial={{ opacity: 0, y: 20 }}
                 whileInView={{ opacity: 1, y: 0 }}
                 viewport={{ once: true, margin: '-80px' }}
-                transition={{ duration: 0.6, delay: i * 0.08, ease: EASE_OUT }}
+                transition={{ duration: 0.3, delay: i * 0.08, ease: EASE_OUT }}
                 className="text-center lg:text-left"
               >
                 <div className={`text-3xl sm:text-4xl md:text-5xl font-black tracking-tight mb-2 ${