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)/about/about-content-v4.tsx

@@ -134,7 +134,7 @@ function MetricsStrip({ data }: { data: AboutData }) {
               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 ${i === 0 ? 'text-brand' : 'text-ink'}`}>
@@ -264,7 +264,7 @@ function MilestonesSection({ data }: { data: AboutData }) {
               initial={{ opacity: 0, x: -20 }}
               whileInView={{ opacity: 1, x: 0 }}
               viewport={{ once: true, margin: '-60px' }}
-              transition={{ duration: 0.6, delay: idx * 0.08, ease: EASE_OUT }}
+              transition={{ duration: 0.3, delay: idx * 0.08, ease: EASE_OUT }}
               className="relative pl-8 sm:pl-12 md:pl-16 pb-10 sm:pb-12 md:pb-14 last:pb-0"
             >
               <div className="absolute left-0 top-2 bottom-0 w-px bg-border-primary last:hidden" />