docs: Add Windows OCR dependencies and fix IIS API error handling

- Add OCR installation instructions for Windows (Poppler, Tesseract, PaddleOCR)
- Add troubleshooting section for common OCR errors on Windows
- Fix web.config.data-entry to use existingResponse="Auto" instead of "Replace"
  This allows FastAPI JSON error responses to pass through IIS unchanged
- Update system requirements to recommend 16GB RAM for OCR workloads

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

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

data-entry-app/README.md

@@ -125,6 +125,61 @@ dnf install -y \
 
 **Note:** PaddleOCR (engine principal) se instaleaza automat cu pip. Tesseract este folosit ca fallback.
 
+### OCR System Dependencies (Windows)
+
+Pe Windows Server trebuie instalate manual urmatoarele componente:
+
+#### 1. Poppler (pentru conversie PDF → imagini)
+
+```powershell
+# Descarca Poppler pentru Windows
+# https://github.com/osborn/poppler-windows/releases
+# sau https://github.com/bblanchon/pdfium-binaries
+
+# Extrage in C:\Program Files\poppler\
+# Adauga la PATH: C:\Program Files\poppler\Library\bin
+```
+
+#### 2. Tesseract OCR (engine OCR backup)
+
+```powershell
+# Descarca installer de la:
+# https://github.com/UB-Mannheim/tesseract/wiki
+
+# Instaleaza cu limbile: English + Romanian
+# Default path: C:\Program Files\Tesseract-OCR\
+# Adauga la PATH
+```
+
+#### 3. Python OCR Dependencies (in venv)
+
+```powershell
+cd C:\inetpub\wwwroot\roa2web\data-entry-backend
+.\venv\Scripts\activate
+
+# Instaleaza dependentele OCR
+pip install paddlepaddle>=2.5.0
+pip install paddleocr>=2.7.0
+pip install opencv-python>=4.8.0
+pip install pytesseract>=0.3.10
+pip install pdf2image>=1.16.0
+
+# Sau din requirements.txt
+pip install -r requirements.txt
+```
+
+#### 4. Restart serviciu
+
+```powershell
+nssm restart ROA2WEB-DataEntry
+```
+
+**Note importante Windows:**
+- Prima rulare PaddleOCR descarca modele (~200MB) - poate dura cateva minute
+- PaddleOCR necesita ~2GB RAM disponibil
+- Verifica PATH-ul pentru Poppler si Tesseract dupa instalare
+- Restart serviciul backend dupa orice modificare PATH
+
 ### OCR API Endpoints
 
 | Method | Endpoint | Description |
@@ -270,6 +325,49 @@ Full API documentation available at http://localhost:8003/docs when backend is r
 2. Install system dependencies (tesseract, poppler)
 3. Verify PaddleOCR installed: `python -c "from paddleocr import PaddleOCR"`
 
+### OCR Windows - "poppler not in PATH"
+
+```powershell
+# Eroare: "Unable to get page count. Is poppler installed and in PATH?"
+
+# Solutie 1: Adauga Poppler la PATH
+# System Properties → Environment Variables → System variables → Path → New
+# Adauga: C:\Program Files\poppler\Library\bin
+
+# Solutie 2: Restart serviciul dupa modificarea PATH
+nssm restart ROA2WEB-DataEntry
+
+# Verificare:
+pdfinfo --version
+```
+
+### OCR Windows - "tesseract not found"
+
+```powershell
+# Eroare: "tesseract is not installed or it's not in your PATH"
+
+# Solutie: Adauga Tesseract la PATH
+# C:\Program Files\Tesseract-OCR\
+
+# Verificare:
+tesseract --version
+tesseract --list-langs  # Trebuie sa arate 'ron' si 'eng'
+```
+
+### OCR Windows - PaddleOCR import error
+
+```powershell
+# Eroare: "No module named 'paddleocr'"
+
+cd C:\inetpub\wwwroot\roa2web\data-entry-backend
+.\venv\Scripts\activate
+pip install paddlepaddle>=2.5.0
+pip install paddleocr>=2.7.0
+
+# Restart serviciu
+nssm restart ROA2WEB-DataEntry
+```
+
 ### Low OCR accuracy
 
 - Ensure good lighting when taking receipt photos