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.

test_print_reporting.py

@@ -0,0 +1,37 @@
+"""Test that the print layer reports failure honestly instead of always True."""
+
+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 print_label import print_to_printer, _sumatra_print, SUMATRA_EXIT_CODES
+
+SUMATRA = os.path.join(os.path.dirname(os.path.abspath(__file__)), "SumatraPDF", "SumatraPDF.exe")
+
+
+def main() -> int:
+    print("1. SumatraPDF exit-code handling")
+    # Nonexistent printer must fail, not silently succeed.
+    ok, message = _sumatra_print(SUMATRA, "NoSuchPrinter_XYZ", "nope.pdf", "noscale")
+    print(f"   missing file + printer -> success={ok}")
+    print(f"   message: {message}")
+    file_missing_ok = not ok
+
+    print("\n2. Documented exit codes are mapped")
+    for code in sorted(SUMATRA_EXIT_CODES):
+        print(f"   {code}: {SUMATRA_EXIT_CODES[code]}")
+
+    print("\n3. print_to_printer on a nonexistent PDF must return False")
+    result = print_to_printer("Brother PT-E560BT", "does_not_exist.pdf", settings="noscale")
+    print(f"   returned: {result}  {'PASS' if result is False else 'FAIL'}")
+
+    print("\n" + "=" * 60)
+    passed = file_missing_ok and result is False
+    print("RESULT:", "PASS" if passed else "FAIL")
+    return 0 if passed else 1
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())