Migrate from Vite to Next.js 15 with SSR

- Replace Vite + React Router with Next.js 15 App Router
- Implement i18n with next-intl (URL-based: /de, /en, /sr)
- Add SSR/SSG for all pages (48 static pages generated)
- Setup Supabase SSR client for auth
- Migrate all pages: Home, About, Portfolio, Blog, Contact, Login, Dashboard, Imprint, Privacy, Terms
- Add Docker support with standalone output
- Replace i18next with next-intl JSON translations
- Use next/image for optimized images

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/lib/supabase/client.ts

@@ -0,0 +1,8 @@
+import { createBrowserClient } from '@supabase/ssr';
+
+export function createClient() {
+  return createBrowserClient(
+    process.env.NEXT_PUBLIC_SUPABASE_URL!,
+    process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY!
+  );
+}

src/lib/supabase/server.ts

@@ -0,0 +1,27 @@
+import { createServerClient } from '@supabase/ssr';
+import { cookies } from 'next/headers';
+
+export async function createClient() {
+  const cookieStore = await cookies();
+
+  return createServerClient(
+    process.env.NEXT_PUBLIC_SUPABASE_URL!,
+    process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY!,
+    {
+      cookies: {
+        getAll() {
+          return cookieStore.getAll();
+        },
+        setAll(cookiesToSet) {
+          try {
+            cookiesToSet.forEach(({ name, value, options }) =>
+              cookieStore.set(name, value, options)
+            );
+          } catch {
+            // Handle server component context
+          }
+        },
+      },
+    }
+  );
+}