Add Windows build scripts and documentation for single-file executable

BUILD_ON_WINDOWS.md

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+# Building LabelPrinter.exe on Windows
+
+This guide explains how to build a standalone `LabelPrinter.exe` single-file executable on a Windows machine.
+
+## Prerequisites
+
+1. **Python 3.10 or higher** - Download from https://www.python.org/
+   - ⚠️ **IMPORTANT**: Check "Add Python to PATH" during installation
+   - Verify: Open Command Prompt and type `python --version`
+
+2. **Git** (optional, for cloning the repository)
+
+3. **Internet connection** - To download dependencies
+
+## Quick Start (Using Provided Scripts)
+
+### Option 1: Batch Script (Recommended for CMD users)
+
+1. Open **Command Prompt** (cmd.exe)
+2. Navigate to the project folder:
+   ```
+   cd C:\path\to\label_print
+   ```
+3. Run the build script:
+   ```
+   build_windows.bat
+   ```
+4. Wait 5-15 minutes for the build to complete
+5. The executable will be in: `dist\LabelPrinter.exe`
+
+### Option 2: PowerShell Script
+
+1. Open **PowerShell** (as Administrator recommended)
+2. Navigate to the project folder:
+   ```
+   cd C:\path\to\label_print
+   ```
+3. Allow script execution (if needed):
+   ```
+   Set-ExecutionPolicy -ExecutionPolicy RemoteSigned -Scope CurrentUser
+   ```
+4. Run the build script:
+   ```
+   .\build_windows.ps1
+   ```
+5. Wait 5-15 minutes for the build to complete
+6. The executable will be in: `dist\LabelPrinter.exe`
+
+## Manual Build Steps
+
+If you prefer to run commands manually:
+
+### Step 1: Prepare Python Environment
+
+```bash
+# Upgrade pip, setuptools, and wheel
+python -m pip install --upgrade pip setuptools wheel
+```
+
+### Step 2: Install Dependencies
+
+```bash
+# Install required Python packages
+pip install python-barcode pillow reportlab kivy==2.2.1 pyinstaller==6.1.0
+```
+
+### Step 3: Build the Executable
+
+```bash
+# Create single-file executable
+pyinstaller label_printer_gui.py ^
+    --onefile ^
+    --windowed ^
+    --name=LabelPrinter ^
+    --distpath=./dist ^
+    --workpath=./build ^
+    --hidden-import=kivy ^
+    --hidden-import=PIL ^
+    --hidden-import=barcode ^
+    --hidden-import=reportlab ^
+    --hidden-import=print_label ^
+    --hidden-import=print_label_pdf ^
+    -y
+```
+
+The build process will take 5-15 minutes depending on your PC speed.
+
+### Step 4: Test the Executable
+
+```bash
+# Run the built executable
+dist\LabelPrinter.exe
+```
+
+## Output
+
+After successful build, you'll have:
+
+```
+dist/
+└── LabelPrinter.exe          ← Single executable file
+```
+
+## Distributing the Executable
+
+You can:
+1. **Copy `LabelPrinter.exe`** to any Windows PC (no Python needed!)
+2. **Share via USB** or file transfer
+3. **Create an installer** using NSIS or InnoSetup (optional)
+4. **Upload to GitHub Releases** for public distribution
+
+## Troubleshooting
+
+### Error: "Python is not recognized"
+- Reinstall Python and check "Add Python to PATH"
+- Restart Command Prompt after reinstalling Python
+
+### Error: "pip command not found"
+- Use `python -m pip` instead of `pip`
+
+### Build takes too long (>30 minutes)
+- **Normal for first build** - Kivy framework is large
+- Subsequent builds will be faster due to caching
+- Close other applications to free up RAM
+
+### Error: "No module named 'kivy'"
+- Make sure dependencies installed correctly: `pip install kivy==2.2.1`
+- Check internet connection
+
+### Error: "LabelPrinter.exe won't start"
+- Make sure all files are in the project folder:
+  - `label_printer_gui.py`
+  - `print_label.py`
+  - `print_label_pdf.py`
+- Antivirus might be blocking it - check security software
+
+## Build Time Reference
+
+- **First build**: 10-15 minutes (downloading dependencies)
+- **Subsequent builds**: 5-10 minutes (cached dependencies)
+
+## Advanced Options
+
+### Reduce Build Time
+```bash
+pyinstaller label_printer_gui.py --onefile --windowed --name=LabelPrinter -y
+```
+
+### Add Icon to Executable
+```bash
+pyinstaller label_printer_gui.py --onefile --windowed --name=LabelPrinter --icon=path\to\icon.ico -y
+```
+
+### Faster: Use --onedir (Directory) instead of --onefile
+```bash
+pyinstaller label_printer_gui.py --onedir --windowed --name=LabelPrinter -y
+# Builds in ~3-5 minutes, but creates a folder instead of single file
+```
+
+## Support
+
+If you encounter issues:
+1. Check the error message carefully
+2. Make sure Python 3.10+ is installed
+3. Verify all dependencies: `pip list`
+4. Check internet connection
+5. Try again with a fresh Command Prompt window