Add P-touch Labels for Asset: 63x20 mm label format for PT-E560BT

New three-column label format for Brother P-touch EDGE PT-E560BT asset tags:
logo | three static lines + variable field | QR code.

Layout and rendering
- ptouch_label.py: geometry engine with PDF and preview renderers. Both
  consume the same geometry, so the preview matches the print exactly.
- Code symbols are snapped to whole printer dots per module. Fractional
  modules are the usual reason a small QR code will not scan.
- QR is maximised to the printable height by default (16.4 mm, 4 dots per
  module) instead of a fixed 16 mm box (12.3 mm, 3 dots per module).
- Code payload is composed as prefix + inventory + suffix. A legacy
  {inventory} template is migrated on first save.

Hardware handling
- print_area.py reads the driver's real printable area via GetDeviceCaps.
  The PT-E560BT head is 128 dots at 180 dpi, so the maximum print height is
  18.06 mm even on 24 mm tape; the driver reports media as 65x24 mm but only
  about 61x18 mm is reachable. Content is fitted to the reachable area,
  otherwise the driver silently crops it.
- set_printer_resolution.py reads/switches the driver's resolution mode. The
  driver offers 180x180 (symmetric) and 180x360 (anisotropic, 2x across the
  tape); the anisotropic mode scaled output incorrectly.

GUI
- label_printer_ptouch_gui.py: 600x300 two-column panel - controls on the
  left, live preview on the right. Advanced settings for logo, static lines,
  code prefix/suffix and error correction.
- native_file_dialog.py: the standard Windows file picker, run in a
  subprocess because Tk and Kivy both want the main event loop.

Printing
- Print failures are reported honestly. print_to_printer previously returned
  True unconditionally, so a failed print claimed success and was logged as
  SUCCESS.
- SumatraPDF exit codes are now checked (4 = no printer, 5 = driver error).
- The PDF is sent with noscale so driver-side scaling cannot distort the QR
  module pitch.

Tests
- validate_ptouch_layout.py decodes the QR back out of the rendered preview
  module by module, proving the preview and PDF are the same layout.
- test_ptouch_pipeline.py writes to a temp config so it cannot overwrite
  operator settings.
- test_gui_layout.py exercises the real app class headlessly.
- test_print_reporting.py covers the failure paths.

Diagnostics: check_print_area.py, check_print_geometry.py, check_devmode.py,
print_calibration.py, print_measure_scale.py, capture_print_job.py.

print_test_label.py

@@ -0,0 +1,56 @@
+"""
+Send one test label to the PT-E560BT.
+
+Generates the 63 x 20 mm label and prints it through SumatraPDF with noscale so
+the QR module pitch reaches the tape unmangled. Reports the real printer exit
+status rather than assuming success.
+"""
+
+import os
+import sys
+
+sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
+os.chdir(os.path.dirname(os.path.abspath(__file__)))
+
+from label_config import load_config, save_config
+from print_label import print_ptouch_label
+from ptouch_label import code_density_warning
+
+PRINTER = "Brother PT-E560BT"
+TEST_INVENTORY = sys.argv[1] if len(sys.argv) > 1 else "INV-0001"
+
+
+def main() -> int:
+    cfg = load_config()
+
+    # Only seed defaults on the very first run so operator settings are kept.
+    if not os.path.exists("label_config.json"):
+        print("No saved settings - writing defaults (edit them in Advanced settings).")
+        cfg.static_lines = ["MOTO ADV SRL", "Articol: CABLU", "Rev: 2026-09"]
+        cfg.qr_prefix = "INV-"
+        save_config(cfg)
+
+    print(f"Printer   : {PRINTER}")
+    print(f"Inventory : {TEST_INVENTORY}")
+    print(f"QR string : {cfg.build_code_payload(TEST_INVENTORY)!r}")
+    print(f"Logo      : {cfg.logo_path or '(none set)'}")
+    print(f"Send opts : {cfg.sumatra_settings}")
+
+    warning = code_density_warning(cfg, TEST_INVENTORY)
+    if warning:
+        print(f"\nWARNING: {warning}")
+
+    print("\nGenerating and printing...")
+    success, pdf_path, warning = print_ptouch_label(TEST_INVENTORY, PRINTER, cfg)
+
+    print("\n" + "=" * 62)
+    print(f"PDF     : {pdf_path}")
+    print(f"Result  : {'SUCCESS' if success else 'FAILED'}")
+    if warning:
+        print(f"Warning : {warning}")
+    print("=" * 62)
+    return 0 if success else 1
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())