[split-required] Split final batch of monoliths >1000 LOC

Python (6 files in klausur-service):
- rbac.py (1,132 → 4), admin_api.py (1,012 → 4)
- routes/eh.py (1,111 → 4), ocr_pipeline_geometry.py (1,105 → 5)

Python (2 files in backend-lehrer):
- unit_api.py (1,226 → 6), game_api.py (1,129 → 5)

Website (6 page files):
- 4x klausur-korrektur pages (1,249-1,328 LOC each) → shared components
  in website/components/klausur-korrektur/ (17 shared files)
- companion (1,057 → 10), magic-help (1,017 → 8)

All re-export barrels preserve backward compatibility.
Zero import errors verified.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

website/components/klausur-korrektur/ErrorBanner.tsx

@@ -0,0 +1,26 @@
+'use client'
+
+/**
+ * Error banner component for displaying dismissible error messages.
+ */
+
+interface ErrorBannerProps {
+  error: string
+  onDismiss: () => void
+}
+
+export default function ErrorBanner({ error, onDismiss }: ErrorBannerProps) {
+  return (
+    <div className="mb-4 p-4 bg-red-50 border border-red-200 rounded-lg flex items-center gap-3">
+      <svg className="w-5 h-5 text-red-600" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+        <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M12 8v4m0 4h.01M21 12a9 9 0 11-18 0 9 9 0 0118 0z" />
+      </svg>
+      <span className="text-red-800">{error}</span>
+      <button onClick={onDismiss} className="ml-auto text-red-600 hover:text-red-800">
+        <svg className="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+          <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M6 18L18 6M6 6l12 12" />
+        </svg>
+      </button>
+    </div>
+  )
+}