Improve GUI and barcode generation

- Update GUI title to 'Label Printing' with white text
- Add character limit (25 chars) to all input fields
- Add number-only filter to quantity field
- Fix barcode generation in PDF module
- Create pdf_backup folder for storing generated PDFs
- Add pdf backup logging and confirmation
- Move demo files and tests to documentation folder
- Reorganize project structure for better clarity

documentation/start_gui.sh

@@ -0,0 +1,52 @@
+#!/bin/bash
+
+# Label Printer GUI - Quick Start Script
+# This script sets up and runs the Label Printer GUI application
+
+set -e
+
+echo "=========================================="
+echo "Label Printer GUI - Setup & Run"
+echo "=========================================="
+echo ""
+
+# Check Python installation
+echo "[1/4] Checking Python installation..."
+if ! command -v python3 &> /dev/null; then
+    echo "❌ Python 3 not found. Please install Python 3.7 or higher."
+    exit 1
+fi
+PYTHON_VERSION=$(python3 --version | cut -d' ' -f2)
+echo "✓ Python $PYTHON_VERSION found"
+echo ""
+
+# Check CUPS
+echo "[2/4] Checking CUPS (printer service)..."
+if ! command -v lpstat &> /dev/null; then
+    echo "⚠ CUPS not found. Please install with: sudo apt-get install cups"
+    echo "  Proceeding anyway - will use PDF printer"
+else
+    echo "✓ CUPS found"
+    echo "  Available printers:"
+    lpstat -p -d | head -5
+fi
+echo ""
+
+# Install dependencies
+echo "[3/4] Installing Python dependencies..."
+if [ -f "requirements_gui.txt" ]; then
+    pip install -r requirements_gui.txt
+    echo "✓ Dependencies installed"
+else
+    echo "⚠ requirements_gui.txt not found"
+    echo "  Installing Kivy and related packages manually..."
+    pip install kivy python-barcode pillow pycups
+fi
+echo ""
+
+# Run the application
+echo "[4/4] Starting Label Printer GUI..."
+echo "=========================================="
+echo ""
+python3 label_printer_gui.py
+