feat: migrate to Next.js 15 App Router with i18n and multi-page SEO

- Replace Vite+React SPA with Next.js 15, TypeScript, App Router
- Static export (output: 'export'), deploy via npm run deploy
- i18n routing: /ru/... and /en/... with generateStaticParams
- New pages: /uslugi/ (catalog), /uslugi/[slug]/ (8 service pages), /faq/, /kontakty/
- SEO: generateMetadata on all pages, JSON-LD Service schema, hreflang alternates
- ContactForm: 'use client', Turnstile + POST to /api/contact.php
- Fonts: Manrope via next/font/google (CSS variable)
- Remove: vite.config.js, entry-server.jsx, prerender scripts, LanguageContext

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/[lang]/layout.tsx

@@ -0,0 +1,34 @@
+import type { Metadata } from 'next'
+import { LOCALES } from '@/lib/i18n'
+import Header from '@/components/layout/Header'
+import Footer from '@/components/layout/Footer'
+import FloatingContacts from '@/components/ui/FloatingContacts'
+import ScrollToTop from '@/components/ui/ScrollToTop'
+
+export function generateStaticParams() {
+  return LOCALES.map(lang => ({ lang }))
+}
+
+export const metadata: Metadata = {
+  title: { default: 'Сисадмингрупп — IT-аутсорсинг в Пушкино', template: '%s | Сисадмингрупп' },
+  description: 'IT-аутсорсинг, техническая поддержка, кибербезопасность для бизнеса в Пушкино и Московской области. Опыт 10+ лет, 150+ клиентов, SLA от 15 минут.',
+}
+
+export default async function LangLayout({
+  children,
+  params,
+}: {
+  children: React.ReactNode
+  params: Promise<{ lang: string }>
+}) {
+  const { lang } = await params
+  return (
+    <>
+      <Header lang={lang} />
+      <main>{children}</main>
+      <Footer lang={lang} />
+      <FloatingContacts />
+      <ScrollToTop />
+    </>
+  )
+}