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

label_app.py

@@ -6,6 +6,7 @@ select, drag to move, arrow keys to nudge, rotate/resize from the side panel.
 
 import json
 import re
+import sys
 import threading
 import tkinter as tk
 from dataclasses import asdict, dataclass, field
@@ -30,11 +31,34 @@ PX_PER_MM = 8
 SETTINGS_PATH = Path.home() / ".config" / "niimprint-label" / "settings.json"
 DEFAULT_ADDR = "94:11:02:66:16:4D"  # your D101 — change in the app, it is remembered
 
+
+def _asset_dir() -> Path:
+    """Bundled assets: next to this file, or inside a PyInstaller bundle."""
+    base = Path(getattr(sys, "_MEIPASS", Path(__file__).resolve().parent))
+    return base / "assets" / "fonts"
+
+
+def _find_font(name: str, *system_dirs: str) -> str:
+    for d in (_asset_dir(), *map(Path, system_dirs)):
+        if (d / name).is_file():
+            return str(d / name)
+    raise FileNotFoundError(
+        f"Font {name} not found (looked in assets/fonts and system dirs)"
+    )
+
+
+_FONT_DIRS = (
+    "/usr/share/fonts/TTF",
+    "/usr/share/fonts/truetype/dejavu",
+    "/usr/share/fonts/noto",
+    "C:/Windows/Fonts",
+    "/Library/Fonts",
+)
 TEXT_FONTS = {
-    "bold": "/usr/share/fonts/TTF/DejaVuSans-Bold.ttf",
-    "regular": "/usr/share/fonts/TTF/DejaVuSans.ttf",
+    "bold": _find_font("DejaVuSans-Bold.ttf", *_FONT_DIRS),
+    "regular": _find_font("DejaVuSans.ttf", *_FONT_DIRS),
 }
-EMOJI_FONT = "/usr/share/fonts/noto/NotoColorEmoji.ttf"
+EMOJI_FONT = _find_font("NotoColorEmoji.ttf", *_FONT_DIRS)
 EMOJI_FONT_SIZE = 109  # Noto Color Emoji is a bitmap font; only this size loads
 EMOJI_GAMMA = 3.0  # >1 darkens emoji so they survive 1-bit dithering
 EMOJI_SCALE = 1.15  # emoji height relative to text size
@@ -612,7 +636,7 @@ class LabelApp(ttk.Window):
         bar.grid(row=5, column=0, sticky="we", pady=(12, 0))
         self.print_btn = ttk.Button(
             bar,
-            text="🖨  Print",
+            text="Print",
             command=self.print_label,
             bootstyle="success",
             width=12,