feat: Improve OCR adaptive pipeline with early exit and better pattern matching

- Add adaptive 3-step OCR pipeline with early exit when all 5 fields found
- Add pattern for "C. I. F." with spaces (OCR artifact from PaddleOCR)
- Add pattern for YYYY. MM. DD date format with spaces (OMV/Petrom receipts)
- Add pattern for "OTAL TAXE" with T cut off and reversed amount position
- Make TVA rate pattern more flexible (code letter optional, handle "-21%")
- Replace logger.info with print(flush=True) for better debugging visibility
- Improve OCRPreview.vue to show extraction progress and raw OCR text

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

data-entry-app/backend/app/main.py

@@ -1,10 +1,19 @@
 """FastAPI application entry point for Data Entry App."""
 
 import sys
+import logging
+import threading
 from pathlib import Path
 from contextlib import asynccontextmanager
 
 from fastapi import FastAPI
+
+# Configure logging to show INFO level messages
+logging.basicConfig(
+    level=logging.INFO,
+    format='%(asctime)s - %(name)s - %(levelname)s - %(message)s',
+    datefmt='%H:%M:%S'
+)
 from fastapi.middleware.cors import CORSMiddleware
 from fastapi.staticfiles import StaticFiles
 
@@ -30,6 +39,18 @@ async def lifespan(app: FastAPI):
     settings.upload_path_resolved
     print(f"Upload path: {settings.upload_path_resolved}")
 
+    # Pre-initialize OCR engine in background (PaddleOCR takes 15-20s)
+    def init_ocr_background():
+        try:
+            from app.services.ocr_service import ocr_service
+            ocr_service.ocr_engine._init_paddle_lazy()
+            print("OCR engine ready")
+        except Exception as e:
+            print(f"Warning: OCR engine pre-load failed: {e}")
+
+    print("Starting OCR engine pre-load (background)...")
+    threading.Thread(target=init_ocr_background, daemon=True).start()
+
     yield
 
     # Shutdown