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>

next.config.ts

@@ -0,0 +1,10 @@
+import type { NextConfig } from 'next'
+
+const nextConfig: NextConfig = {
+  output: 'export',
+  distDir: process.env.BUILD_DIR || 'out',
+  trailingSlash: true,
+  images: { unoptimized: true },
+}
+
+export default nextConfig