fix(ocr-pipeline): increase LLM timeout to 300s and disable qwen3 thinking

- Add /no_think tag to prompt (qwen3 thinking mode causes massive slowdown)
- Increase httpx timeout from 120s to 300s for large vocab tables
- Improve error logging with traceback and exception type

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

klausur-service/backend/ocr_pipeline_api.py

@@ -1420,8 +1420,9 @@ async def run_llm_review(session_id: str, request: Request):
     try:
         result = await llm_review_entries(entries, model=model)
     except Exception as e:
-        logger.error(f"LLM review failed for session {session_id}: {e}")
-        raise HTTPException(status_code=502, detail=f"LLM review failed: {e}")
+        import traceback
+        logger.error(f"LLM review failed for session {session_id}: {type(e).__name__}: {e}\n{traceback.format_exc()}")
+        raise HTTPException(status_code=502, detail=f"LLM review failed ({type(e).__name__}): {e}")
 
     # Store result inside word_result as a sub-key
     word_result["llm_review"] = {