Tailwind v4 migration, massive SEO optimization, and fixes

- Migrate to Tailwind CSS v4 with @theme, @layer, @plugin syntax
- Upgrade to Next.js 16.1, React 19.2, TypeScript 5.9.3
- Add 8 technology landing pages (Next.js, React, TypeScript, Tailwind CSS, Claude AI, Python, n8n, KI-Agenten)
- Expand SEO keywords across all locales (de/en/sr) for home, layout, cities, services
- Add tech-specific keywords to all 22 city pages
- Add FAQ schema + seoKeywords to service detail pages
- Add CollectionPage JSON-LD to blog listing
- Fix city page: dynamic region, BASE_URL canonicals, x-default hreflang
- Rewrite terms page with full German AGB, English and Serbian translations
- Remove dead crypto import and unused CSRF middleware (Edge Runtime fix)
- Remove crawlDelay from robots.ts
- Update sitemap with technology pages (~198 indexed URLs)
- Remove deprecated tailwind.config.js

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

next-env.d.ts

@@ -1,6 +1,6 @@
 /// <reference types="next" />
 /// <reference types="next/image-types/global" />
-/// <reference path="./.next/types/routes.d.ts" />
+import "./.next/types/routes.d.ts";
 
 // NOTE: This file should not be edited
 // see https://nextjs.org/docs/app/api-reference/config/typescript for more information.