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/lib/content.ts

@@ -2,12 +2,28 @@ import { getSiteContent } from "@/lib/db";
 import { siteContent as fallback } from "@/data/content";
 import type { SiteContent } from "@/types/content";
 
+let cached: { data: SiteContent; expiresAt: number } | null = null;
+const CACHE_TTL = 5 * 60 * 1000; // 5 minutes
+
 export function getContent(): SiteContent {
+  const now = Date.now();
+  if (cached && now < cached.expiresAt) {
+    return cached.data;
+  }
+
   try {
     const content = getSiteContent();
-    if (content) return content;
+    if (content) {
+      cached = { data: content, expiresAt: now + CACHE_TTL };
+      return content;
+    }
     return fallback;
   } catch {
     return fallback;
   }
 }
+
+/** Invalidate the content cache (call after admin edits). */
+export function invalidateContentCache() {
+  cached = null;
+}