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/app/api/open-day-register/route.ts

@@ -6,6 +6,7 @@ import {
   getOpenDayEvent,
 } from "@/lib/db";
 import { checkRateLimit, getClientIp } from "@/lib/rateLimit";
+import { sanitizeName, sanitizePhone, sanitizeHandle } from "@/lib/validation";
 
 export async function POST(request: NextRequest) {
   const ip = getClientIp(request);
@@ -20,17 +21,18 @@ export async function POST(request: NextRequest) {
     const body = await request.json();
     const { classId, eventId, name, phone, instagram, telegram } = body;
 
-    if (!classId || !eventId || !name || !phone) {
-      return NextResponse.json({ error: "classId, eventId, name, phone are required" }, { status: 400 });
+    if (!classId || !eventId) {
+      return NextResponse.json({ error: "classId and eventId are required" }, { status: 400 });
     }
 
-    const cleanName = (name as string).trim().slice(0, 100);
-    const cleanPhone = (phone as string).replace(/\D/g, "").slice(0, 15);
-    const cleanIg = instagram ? (instagram as string).trim().slice(0, 100) : undefined;
-    const cleanTg = telegram ? (telegram as string).trim().slice(0, 100) : undefined;
+    const cleanName = sanitizeName(name);
+    if (!cleanName) {
+      return NextResponse.json({ error: "Имя обязательно" }, { status: 400 });
+    }
 
+    const cleanPhone = sanitizePhone(phone);
     if (!cleanPhone) {
-      return NextResponse.json({ error: "Invalid phone" }, { status: 400 });
+      return NextResponse.json({ error: "Телефон обязателен" }, { status: 400 });
     }
 
     // Check not already booked
@@ -41,8 +43,8 @@ export async function POST(request: NextRequest) {
     const id = addOpenDayBooking(classId, eventId, {
       name: cleanName,
       phone: cleanPhone,
-      instagram: cleanIg,
-      telegram: cleanTg,
+      instagram: sanitizeHandle(instagram),
+      telegram: sanitizeHandle(telegram),
     });
 
     // Return total bookings for this person (for discount calculation)