feat: Persistente Sessions (PostgreSQL) + Spaltenerkennung (Step 3)

Sessions werden jetzt in PostgreSQL gespeichert statt in-memory.
Neue Session-Liste mit Name, Datum, Schritt. Sessions ueberleben
Browser-Refresh und Container-Neustart. Step 3 nutzt analyze_layout()
fuer automatische Spaltenerkennung mit farbigem Overlay.

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

admin-lehrer/components/ocr-pipeline/StepDeskew.tsx

@@ -22,6 +22,7 @@ export function StepDeskew({ sessionId: existingSessionId, onNext }: StepDeskewP
   const [showGrid, setShowGrid] = useState(true)
   const [error, setError] = useState<string | null>(null)
   const [dragOver, setDragOver] = useState(false)
+  const [sessionName, setSessionName] = useState('')
 
   // Reload session data when navigating back from a later step
   useEffect(() => {
@@ -67,6 +68,9 @@ export function StepDeskew({ sessionId: existingSessionId, onNext }: StepDeskewP
     try {
       const formData = new FormData()
       formData.append('file', file)
+      if (sessionName.trim()) {
+        formData.append('name', sessionName.trim())
+      }
 
       const res = await fetch(`${KLAUSUR_API}/api/v1/ocr-pipeline/sessions`, {
         method: 'POST',
@@ -167,6 +171,20 @@ export function StepDeskew({ sessionId: existingSessionId, onNext }: StepDeskewP
   if (!session) {
     return (
       <div className="space-y-4">
+        {/* Session name input */}
+        <div>
+          <label className="block text-sm font-medium text-gray-600 dark:text-gray-400 mb-1">
+            Session-Name (optional)
+          </label>
+          <input
+            type="text"
+            value={sessionName}
+            onChange={(e) => setSessionName(e.target.value)}
+            placeholder="z.B. Unit 3 Seite 42"
+            className="w-full max-w-sm px-3 py-2 text-sm border rounded-lg dark:bg-gray-800 dark:border-gray-600 dark:text-gray-200 focus:outline-none focus:ring-2 focus:ring-teal-500"
+          />
+        </div>
+
         <div
           onDragOver={(e) => { e.preventDefault(); setDragOver(true) }}
           onDragLeave={() => setDragOver(false)}