Add PyInstaller packaging for Windows and Linux

- label_app.spec: one-file build bundling fonts, emoji data, ttkbootstrap
  themes and (on Windows) fribidi.dll so Pillow can shape emoji sequences
- build-windows.ps1 helper; assets/icon.ico app icon
- Fonts resolved from assets/fonts first, then system dirs, so the app
  runs from a bundle or a checkout on any OS
- Bump Pillow pin to 12.3

readme.md

@@ -149,6 +149,27 @@ printer.print_image(image, density=density, model="d101")
 
 `prepare_print` clamps density to the model's maximum, rotates, and raises `ValueError` if the image is wider than the print head. `print_image` raises `PrinterError` if the printer stops responding or rejects a command.
 
+## Standalone executable (Windows / Linux)
+
+A PyInstaller spec (`label_app.spec`) bundles the app, fonts, emoji data and themes into a single file. Build on the target OS — PyInstaller does not cross-compile.
+
+**Windows** (PowerShell, with Python 3.10+ from python.org):
+
+```
+.\build-windows.ps1
+```
+
+produces `dist\NiimbotLabel.exe` (~30 MB, no installation needed). Bluetooth uses the Windows RFCOMM socket API, so pair the printer in Windows Bluetooth settings first, then enter its MAC address in the app. For USB, enter the `COMx` port or leave the address blank to auto-detect.
+
+`assets/win/fribidi.dll` is bundled because Pillow's Windows wheel needs it for emoji sequences (flags, skin tones, 🧑‍💻-style ZWJ emoji); see `assets/win/README.md`.
+
+**Linux**:
+
+```
+.venv/bin/pip install pyinstaller
+.venv/bin/pyinstaller --noconfirm label_app.spec   # -> dist/NiimbotLabel
+```
+
 ## Licence
 
 [MIT](https://choosealicense.com/licenses/mit/). Originally developed by [kjy00302](https://github.com/kjy00302), forked & enhanced by [AndBondStyle](https://github.com/AndBondStyle)