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>

src/index.css

@@ -1,7 +1,8 @@
-@import './colors.css';
-@tailwind base;
-@tailwind components;
-@tailwind utilities;
+@import "tailwindcss";
+@plugin "tailwindcss-animate";
+@plugin "@tailwindcss/forms" {
+  strategy: class;
+}
 
 /* Font loading states */
 html.fonts-loading body {
@@ -27,7 +28,7 @@ html.fonts-fallback body {
     @apply text-foreground antialiased;
     background-color: transparent !important;
   }
-  
+
   #root {
     background-color: transparent !important;
   }
@@ -59,7 +60,7 @@ html.fonts-fallback body {
   .text-gradient {
     @apply bg-clip-text text-transparent bg-gradient-to-r from-primary via-accent to-secondary;
   }
-  
+
   /* GPU acceleration utilities - simplified */
   .gpu-accelerated {
     transform: translateZ(0);
@@ -161,4 +162,4 @@ a, button {
   a {
     @apply min-h-[44px] min-w-[44px];
   }
-}
+}