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/group-booking/route.ts

@@ -1,6 +1,7 @@
 import { NextRequest, NextResponse } from "next/server";
 import { addGroupBooking } from "@/lib/db";
 import { checkRateLimit, getClientIp } from "@/lib/rateLimit";
+import { sanitizeName, sanitizePhone, sanitizeHandle, sanitizeText } from "@/lib/validation";
 
 export async function POST(request: NextRequest) {
   const ip = getClientIp(request);
@@ -15,17 +16,23 @@ export async function POST(request: NextRequest) {
     const body = await request.json();
     const { name, phone, groupInfo, instagram, telegram } = body;
 
-    if (!name || typeof name !== "string" || !phone || typeof phone !== "string") {
-      return NextResponse.json({ error: "name and phone are required" }, { status: 400 });
+    const cleanName = sanitizeName(name);
+    if (!cleanName) {
+      return NextResponse.json({ error: "Имя обязательно" }, { status: 400 });
     }
 
-    const cleanName = name.trim().slice(0, 100);
-    const cleanPhone = phone.trim().slice(0, 30);
-    const cleanGroup = typeof groupInfo === "string" ? groupInfo.trim().slice(0, 200) : undefined;
-    const cleanIg = typeof instagram === "string" ? instagram.trim().slice(0, 100) : undefined;
-    const cleanTg = typeof telegram === "string" ? telegram.trim().slice(0, 100) : undefined;
+    const cleanPhone = sanitizePhone(phone);
+    if (!cleanPhone) {
+      return NextResponse.json({ error: "Телефон обязателен" }, { status: 400 });
+    }
 
-    const id = addGroupBooking(cleanName, cleanPhone, cleanGroup, cleanIg, cleanTg);
+    const id = addGroupBooking(
+      cleanName,
+      cleanPhone,
+      sanitizeText(groupInfo),
+      sanitizeHandle(instagram),
+      sanitizeHandle(telegram)
+    );
     return NextResponse.json({ ok: true, id });
   } catch (err) {
     console.error("[group-booking] POST error:", err);