Fix Academy page crash: optional chaining for byStatus and categoryInfo fallback

- statistics.byStatus.in_progress could crash on empty object → optional chaining
- COURSE_CATEGORY_INFO[course.category] could return undefined → fallback to 'custom'
- Update LLM model to qwen3.5:35b-a3b in docker-compose.yml

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

admin-compliance/app/(sdk)/sdk/academy/page.tsx

@@ -125,7 +125,7 @@ function StatCard({
 }
 
 function CourseCard({ course, enrollmentCount }: { course: Course; enrollmentCount: number }) {
-  const categoryInfo = COURSE_CATEGORY_INFO[course.category]
+  const categoryInfo = COURSE_CATEGORY_INFO[course.category] || COURSE_CATEGORY_INFO['custom']
 
   return (
     <Link href={`/sdk/academy/${course.id}`}>
@@ -589,7 +589,7 @@ export default function AcademyPage() {
               />
               <StatCard
                 label="Aktive Teilnehmer"
-                value={statistics.byStatus.in_progress + statistics.byStatus.not_started}
+                value={(statistics.byStatus?.in_progress || 0) + (statistics.byStatus?.not_started || 0)}
                 color="blue"
               />
               <StatCard