feat: OCR Pipeline mit 6-Schritt-Wizard fuer Seitenrekonstruktion

Neue Route /ai/ocr-pipeline mit schrittweiser Begradigung (Deskew),
Raster-Overlay und Ground Truth. Schritte 2-6 als Platzhalter.

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

klausur-service/backend/main.py

@@ -42,6 +42,7 @@ try:
 except ImportError:
     trocr_router = None
 from vocab_worksheet_api import router as vocab_router, set_db_pool as set_vocab_db_pool, _init_vocab_table, _load_all_sessions, DATABASE_URL as VOCAB_DATABASE_URL
+from ocr_pipeline_api import router as ocr_pipeline_router
 try:
     from dsfa_rag_api import router as dsfa_rag_router, set_db_pool as set_dsfa_db_pool
     from dsfa_corpus_ingestion import DSFAQdrantService, DATABASE_URL as DSFA_DATABASE_URL
@@ -150,6 +151,7 @@ app.include_router(mail_router)       # Unified Inbox Mail
 if trocr_router:
     app.include_router(trocr_router)      # TrOCR Handwriting OCR
 app.include_router(vocab_router)      # Vocabulary Worksheet Generator
+app.include_router(ocr_pipeline_router)  # OCR Pipeline (step-by-step)
 if dsfa_rag_router:
     app.include_router(dsfa_rag_router)   # DSFA RAG Corpus Search