fix: MEDIUM priority — shared validation, content caching, Schedule useReducer, stable keys

- Extract shared sanitization to src/lib/validation.ts, apply to all 3 registration routes (#2)
- Replace key={index} with stable keys in About and News (#4)
- Add 5-min in-memory content cache in content.ts, invalidate on admin section save (#6)
- Refactor Schedule from 8 useState calls to useReducer — single dispatch, fewer re-renders (#8)
- Remove Hero scroll indicator, add auto-scroll to next section on wheel/swipe

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/components/sections/About.tsx

@@ -30,8 +30,8 @@ export function About({ data: about, stats }: AboutProps) {
         </Reveal>
 
         <div className="mt-14 mx-auto max-w-2xl space-y-8 text-center">
-          {about.paragraphs.map((text, i) => (
-            <Reveal key={i}>
+          {about.paragraphs.map((text) => (
+            <Reveal key={text}>
               <p className="text-xl leading-relaxed text-neutral-600 dark:text-neutral-300 sm:text-2xl">
                 {text}
               </p>