fix(locale): align all English MDX page links and add automated links validation test to prevent language drift

tests/mdx-links.test.ts

@@ -0,0 +1,26 @@
+import { describe, it, expect } from 'vitest';
+import fs from 'fs';
+import path from 'path';
+
+describe('English MDX Content Links', () => {
+  it('should not contain German slug routes like /en/kontakt or /en/karriere', () => {
+    const enContentDir = path.join(process.cwd(), 'content', 'en');
+    const files = fs.readdirSync(enContentDir).filter(f => f.endsWith('.mdx'));
+
+    const forbiddenLinks = ['/en/kontakt', '/en/karriere'];
+    const infractions: string[] = [];
+
+    files.forEach(file => {
+      const filePath = path.join(enContentDir, file);
+      const content = fs.readFileSync(filePath, 'utf8');
+
+      forbiddenLinks.forEach(link => {
+        if (content.includes(link)) {
+          infractions.push(`${file} contains forbidden link "${link}"`);
+        }
+      });
+    });
+
+    expect(infractions).toEqual([]);
+  });
+});