feat(klausur-service): Add Tesseract OCR, DSFA RAG, TrOCR, grid detection and vocab session store

New modules:
- tesseract_vocab_extractor.py: Bounding-box OCR with multi-PSM pipeline
- grid_detection_service.py: CV-based grid/table detection for worksheets
- vocab_session_store.py: PostgreSQL persistence for vocab sessions
- trocr_api.py: TrOCR handwriting recognition endpoint
- dsfa_rag_api.py + dsfa_corpus_ingestion.py: DSFA RAG corpus search

Changes:
- Dockerfile: Install tesseract-ocr + deu/eng language packs
- requirements.txt: Add PyMuPDF, pytesseract, Pillow
- main.py: Register new routers, init DB pools + Qdrant collections

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

klausur-service/backend/main.py

@@ -20,6 +20,7 @@ This is the main entry point. All functionality is organized in modular packages
 import os
 from contextlib import asynccontextmanager
 
+import asyncpg
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 from fastapi.staticfiles import StaticFiles
@@ -36,7 +37,19 @@ from admin_api import router as admin_router
 from zeugnis_api import router as zeugnis_router
 from training_api import router as training_router
 from mail.api import router as mail_router
-from trocr_api import router as trocr_router
+try:
+    from trocr_api import router as trocr_router
+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
+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
+except ImportError:
+    dsfa_rag_router = None
+    set_dsfa_db_pool = None
+    DSFAQdrantService = None
+    DSFA_DATABASE_URL = None
 
 # BYOEH Qdrant initialization
 from qdrant_service import init_qdrant_collection
@@ -51,12 +64,42 @@ async def lifespan(app: FastAPI):
     """Application lifespan manager for startup and shutdown events."""
     print("Klausur-Service starting...")
 
+    # Initialize database pool for Vocab Sessions
+    vocab_db_pool = None
+    try:
+        vocab_db_pool = await asyncpg.create_pool(VOCAB_DATABASE_URL, min_size=2, max_size=5)
+        set_vocab_db_pool(vocab_db_pool)
+        await _init_vocab_table()
+        await _load_all_sessions()
+        print(f"Vocab sessions database initialized")
+    except Exception as e:
+        print(f"Warning: Vocab sessions database initialization failed: {e}")
+
+    # Initialize database pool for DSFA RAG
+    dsfa_db_pool = None
+    if DSFA_DATABASE_URL and set_dsfa_db_pool:
+        try:
+            dsfa_db_pool = await asyncpg.create_pool(DSFA_DATABASE_URL, min_size=2, max_size=10)
+            set_dsfa_db_pool(dsfa_db_pool)
+            print(f"DSFA database pool initialized: {DSFA_DATABASE_URL}")
+        except Exception as e:
+            print(f"Warning: DSFA database pool initialization failed: {e}")
+
     # Initialize Qdrant collection for BYOEH
     try:
         await init_qdrant_collection()
         print("Qdrant BYOEH collection initialized")
     except Exception as e:
-        print(f"Warning: Qdrant initialization failed: {e}")
+        print(f"Warning: Qdrant BYOEH initialization failed: {e}")
+
+    # Initialize Qdrant collection for DSFA RAG
+    if DSFAQdrantService:
+        try:
+            dsfa_qdrant = DSFAQdrantService()
+            await dsfa_qdrant.ensure_collection()
+            print("Qdrant DSFA corpus collection initialized")
+        except Exception as e:
+            print(f"Warning: Qdrant DSFA initialization failed: {e}")
 
     # Ensure EH upload directory exists
     os.makedirs(EH_UPLOAD_DIR, exist_ok=True)
@@ -65,6 +108,16 @@ async def lifespan(app: FastAPI):
 
     print("Klausur-Service shutting down...")
 
+    # Close Vocab sessions database pool
+    if vocab_db_pool:
+        await vocab_db_pool.close()
+        print("Vocab sessions database pool closed")
+
+    # Close DSFA database pool
+    if dsfa_db_pool:
+        await dsfa_db_pool.close()
+        print("DSFA database pool closed")
+
 
 app = FastAPI(
     title="Klausur-Service",
@@ -94,7 +147,11 @@ app.include_router(admin_router)      # NiBiS Ingestion
 app.include_router(zeugnis_router)    # Zeugnis Rights-Aware Crawler
 app.include_router(training_router)   # Training Management
 app.include_router(mail_router)       # Unified Inbox Mail
-app.include_router(trocr_router)      # TrOCR Handwriting OCR
+if trocr_router:
+    app.include_router(trocr_router)      # TrOCR Handwriting OCR
+app.include_router(vocab_router)      # Vocabulary Worksheet Generator
+if dsfa_rag_router:
+    app.include_router(dsfa_rag_router)   # DSFA RAG Corpus Search
 
 
 # =============================================