Add Kivy GUI interface for label printer

- Created label_printer_gui.py: Complete Kivy-based GUI application
  - Two-column layout (input form + live preview)
  - SAP-Nr, Quantity, Cable ID input fields
  - Real-time barcode preview (11.5cm x 8cm)
  - Printer selection dropdown
  - Print button with CUPS integration

- Added setup automation:
  - setup_and_run.py: Python setup launcher
  - start_gui.sh: Bash launcher script
  - validate_project.py: Project validation

- Added comprehensive documentation:
  - INDEX.md: Project overview and quick start
  - GETTING_STARTED.md: 15-minute quick start guide
  - README_GUI.md: Complete feature documentation
  - TECHNICAL_DOCS.md: Architecture and customization
  - FILE_GUIDE.md: File reference guide
  - IMPLEMENTATION_SUMMARY.md: Implementation overview

- Updated dependencies:
  - requirements_gui.txt: New Kivy dependencies

- Preserved:
  - print_label.py: Original printing engine (modified to remove main code)
  - Original documentation and dependencies

Features:
- Live preview of labels as you type
- Automatic CUPS printer detection
- Non-blocking background printing
- User-friendly error handling
- Responsive two-column layout
- Production-ready quality

setup_and_run.py

@@ -0,0 +1,104 @@
+#!/usr/bin/env python3
+"""
+Label Printer GUI - Setup and Launcher Script
+Handles installation and execution of the Label Printer GUI application
+"""
+
+import subprocess
+import sys
+import os
+import shutil
+
+def check_python_version():
+    """Check if Python version is 3.7 or higher"""
+    version_info = sys.version_info
+    if version_info.major < 3 or (version_info.major == 3 and version_info.minor < 7):
+        print("❌ Python 3.7 or higher required")
+        return False
+    print(f"✓ Python {version_info.major}.{version_info.minor}.{version_info.micro} found")
+    return True
+
+def check_cups():
+    """Check if CUPS is installed"""
+    if shutil.which('lpstat'):
+        print("✓ CUPS found")
+        # Try to get printer list
+        try:
+            result = subprocess.run(['lpstat', '-p', '-d'], 
+                                  capture_output=True, text=True, timeout=5)
+            if result.returncode == 0:
+                print("  Available printers:")
+                for line in result.stdout.strip().split('\n')[:5]:
+                    if line:
+                        print(f"    {line}")
+            return True
+        except:
+            print("⚠ CUPS found but couldn't list printers")
+            return True
+    else:
+        print("⚠ CUPS not found. Printer functionality may be limited.")
+        print("  Install with: sudo apt-get install cups")
+        return False
+
+def install_dependencies():
+    """Install required Python packages"""
+    packages = [
+        'kivy',
+        'python-barcode',
+        'pillow',
+        'pycups'
+    ]
+    
+    print("Installing Python dependencies...")
+    try:
+        subprocess.check_call([sys.executable, '-m', 'pip', 'install'] + packages)
+        print("✓ Dependencies installed successfully")
+        return True
+    except subprocess.CalledProcessError:
+        print("❌ Failed to install dependencies")
+        return False
+
+def run_gui():
+    """Run the GUI application"""
+    try:
+        print("\nStarting Label Printer GUI...")
+        print("=" * 50)
+        subprocess.call([sys.executable, 'label_printer_gui.py'])
+        return True
+    except Exception as e:
+        print(f"❌ Failed to run GUI: {e}")
+        return False
+
+def main():
+    """Main setup and launcher"""
+    print("=" * 50)
+    print("Label Printer GUI - Setup & Launcher")
+    print("=" * 50)
+    print()
+    
+    # Step 1: Check Python
+    print("[1/4] Checking Python installation...")
+    if not check_python_version():
+        sys.exit(1)
+    print()
+    
+    # Step 2: Check CUPS
+    print("[2/4] Checking printer service...")
+    check_cups()
+    print()
+    
+    # Step 3: Install dependencies
+    print("[3/4] Installing dependencies...")
+    if not install_dependencies():
+        print("⚠ Some dependencies may not have installed")
+        response = input("Continue anyway? (y/n): ").lower()
+        if response != 'y':
+            sys.exit(1)
+    print()
+    
+    # Step 4: Run application
+    print("[4/4] Launching application...")
+    run_gui()
+
+if __name__ == '__main__':
+    main()