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/validation.ts

@@ -0,0 +1,27 @@
+/**
+ * Shared input sanitization for public registration endpoints.
+ */
+
+export function sanitizeName(name: unknown): string | null {
+  if (!name || typeof name !== "string") return null;
+  const clean = name.trim().slice(0, 100);
+  return clean || null;
+}
+
+export function sanitizePhone(phone: unknown): string | null {
+  if (!phone || typeof phone !== "string") return null;
+  const clean = phone.replace(/\D/g, "").slice(0, 15);
+  return clean.length >= 9 ? clean : null;
+}
+
+export function sanitizeHandle(value: unknown): string | undefined {
+  if (!value || typeof value !== "string") return undefined;
+  const clean = value.trim().slice(0, 100);
+  return clean || undefined;
+}
+
+export function sanitizeText(value: unknown, maxLength: number = 200): string | undefined {
+  if (!value || typeof value !== "string") return undefined;
+  const clean = value.trim().slice(0, maxLength);
+  return clean || undefined;
+}