feat: Implement page-split step with auto-detection and sub-session naming

StepPageSplit now:
- Auto-calls POST /page-split on step entry
- Shows oriented image + detection result
- If double page: creates sub-sessions named "Title — S. 1/2"
- If single page: green badge "keine Trennung noetig"
- Manual "Weiter" button (no auto-advance)

Also:
- StepOrientation wrapper simplified (no page-split in orientation)
- StepUpload passes name back via onUploaded(sid, name)
- page.tsx: after page-split "Weiter" switches to first sub-session
- useKombiPipeline exposes setSessionName

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

admin-lehrer/app/(admin)/ai/ocr-kombi/page.tsx

@@ -40,9 +40,9 @@ function OcrKombiContent() {
     deleteSession,
     renameSession,
     updateCategory,
-    handleOrientationComplete,
     handleSessionChange,
     setSessionId,
+    setSessionName,
     setSubSessions,
     setParentSessionId,
     setIsGroundTruth,
@@ -54,8 +54,9 @@ function OcrKombiContent() {
         return (
           <StepUpload
             sessionId={sessionId}
-            onUploaded={(sid) => {
+            onUploaded={(sid, name) => {
               setSessionId(sid)
+              setSessionName(name)
               loadSessions()
             }}
             onNext={handleNext}
@@ -65,7 +66,7 @@ function OcrKombiContent() {
         return (
           <StepOrientation
             sessionId={sessionId}
-            onNext={handleOrientationComplete}
+            onNext={() => handleNext()}
             onSessionList={() => { loadSessions(); handleNewSession() }}
           />
         )
@@ -73,10 +74,19 @@ function OcrKombiContent() {
         return (
           <StepPageSplit
             sessionId={sessionId}
-            onNext={handleNext}
+            sessionName={sessionName}
+            onNext={() => {
+              // If sub-sessions were created, switch to the first one
+              if (subSessions.length > 0) {
+                setSessionId(subSessions[0].id)
+                setSessionName(subSessions[0].name)
+              }
+              handleNext()
+            }}
             onSubSessionsCreated={(subs) => {
               setSubSessions(subs)
               if (sessionId) setParentSessionId(sessionId)
+              loadSessions()
             }}
           />
         )

admin-lehrer/app/(admin)/ai/ocr-kombi/useKombiPipeline.ts

@@ -356,6 +356,7 @@ export function useKombiPipeline() {
     setSessionId,
     setSubSessions,
     setParentSessionId,
+    setSessionName,
     setIsGroundTruth,
   }
 }