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.

check_devmode.py

@@ -0,0 +1,99 @@
+"""
+Dump the full DEVMODE of the PT-E560BT driver.
+
+The printed length is far shorter than the page we send, which suggests the
+driver is cropped or scaled by a setting of its own. This prints every field
+that could cause that, so the behaviour can be explained rather than guessed.
+"""
+
+import win32print
+
+PRINTER = "Brother PT-E560BT"
+
+ORIENTATION = {1: "portrait", 2: "landscape"}
+
+FIELDS_OF_INTEREST = [
+    "PaperSize",
+    "PaperLength",
+    "PaperWidth",
+    "Orientation",
+    "Scale",
+    "Copies",
+    "DefaultSource",
+    "PrintQuality",
+    "Color",
+    "Duplex",
+    "TTOption",
+    "Collate",
+    "FormName",
+    "LogPixels",
+    "BitsPerPel",
+    "Nup",
+    "DisplayFlags",
+    "DisplayFrequency",
+    "ICMMethod",
+    "ICMIntent",
+    "MediaType",
+    "DitherType",
+    "Reserved1",
+    "Reserved2",
+    "PanningWidth",
+    "PanningHeight",
+]
+
+
+def main() -> int:
+    info = win32print.GetPrinter(win32print.OpenPrinter(PRINTER), 2)
+    dm = info.get("pDevMode")
+
+    print(f"Printer   : {PRINTER}")
+    print(f"Driver    : {info.get('pDriverName')}")
+    print(f"Port      : {info.get('pPortName')}")
+
+    print(f"\nDEVMODE size       : {dm.Size} bytes")
+    print(f"DriverExtra        : {dm.DriverExtra} bytes")
+    print(f"Fields set (bitset): 0x{dm.Fields:x}")
+
+    print("\nFields of interest:")
+    for name in FIELDS_OF_INTEREST:
+        if not hasattr(dm, name):
+            continue
+        try:
+            value = getattr(dm, name)
+        except Exception as exc:  # noqa: BLE001
+            print(f"  {name:<18}: <error {exc}>")
+            continue
+        extra = ""
+        if name == "Orientation":
+            extra = f"  ({ORIENTATION.get(value, '?')})"
+        elif name in ("PaperLength", "PaperWidth") and isinstance(value, int):
+            extra = f"  ({value / 10:.1f} mm)"
+        print(f"  {name:<18}: {value}{extra}")
+
+    # Any other integer attributes the struct exposes.
+    print("\nAll remaining numeric fields:")
+    shown = set(FIELDS_OF_INTEREST)
+    for name in sorted(dir(type(dm))):
+        if name.startswith("_") or name in shown:
+            continue
+        try:
+            value = getattr(dm, name)
+        except Exception:  # noqa: BLE001
+            continue
+        if isinstance(value, int) and value != 0:
+            print(f"  {name:<20}: {value}")
+
+    # Explain the relationship between page, printable area and paper length.
+    print("\nInterpretation:")
+    pl = dm.PaperLength / 10
+    pw = dm.PaperWidth / 10
+    print(f"  paper wxh as stored : {pw:.1f} x {pl:.1f} mm "
+          f"(orientation {ORIENTATION.get(dm.Orientation, '?')})")
+    if dm.Orientation == 2:
+        print(f"  rotated for printing: {pl:.1f} mm along tape x {pw:.1f} mm across")
+    print(f"  dmScale             : {dm.Scale}% (100 = no driver scaling)")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())