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_measure_scale.py

@@ -0,0 +1,142 @@
+"""
+Print a measuring label to determine the printer's actual scale factors.
+
+The problem: we render a correct 61 x 18 mm label, but it prints around 25 x 17 mm.
+Two candidate causes predict different numbers, and both look similar at that size:
+
+  (a) Resolution mismatch - the driver reports LOGPIXELSX=360 but the device is
+      180 dpi, so content is compressed 2x along the tape. Predicts marks 10 mm
+      apart appearing ~5 mm apart in X only.
+  (b) Driver shrink-to-fit across the 24 mm media width. Predicts an equal
+      shrink in X and Y: scale 24/65.05 = 0.37 -> marks 10 mm apart appear 3.7 mm.
+
+This label makes the answer unambiguous: it draws ruler ticks at known spacings
+in both axes, so reading one number off the tape identifies the cause.
+
+Reading the print:
+  * X ticks (along the tape) are laid out every 10 mm from 0 to 60.
+  * Y ticks (across the tape) are laid out every 2 mm from 0 to 18.
+  * A 10 x 10 mm reference square sits at a known position.
+
+Measure the distance between tick "0" and tick "60" (intended 60 mm):
+    ~60 mm  -> geometry correct; the problem lies elsewhere
+    ~30 mm  -> case (a), 2x compression along the tape
+    ~22 mm  -> case (b), shrink-to-fit on width
+    other   -> report the measured value
+"""
+
+from __future__ import annotations
+
+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 reportlab.lib.units import mm
+from reportlab.pdfgen import canvas
+
+from label_config import load_config
+from print_area import query_print_area
+from ptouch_label import LabelConfig
+
+PRINTER = "Brother PT-E560BT"
+
+
+def build_measure_pdf(cfg: LabelConfig, path: str) -> str:
+    """Draw the measuring label at the configured content size."""
+    page_w, page_h = cfg.page_size_mm
+    ox, oy = cfg.origin_mm
+    content_w, content_h = cfg.page_width_mm, cfg.page_height_mm
+
+    c = canvas.Canvas(path, pagesize=(page_w * mm, page_h * mm))
+    c.setTitle("PT-E560BT scale measurement")
+
+    def X(v: float) -> float:
+        return (ox + v) * mm
+
+    def Y(v: float) -> float:
+        return (oy + v) * mm
+
+    # Outer frame exactly at the content bounds.
+    c.setStrokeColorRGB(0, 0, 0)
+    c.setLineWidth(0.4)
+    c.rect(X(0), Y(0), content_w * mm, content_h * mm)
+
+    # X ruler: a tick every 10 mm along the bottom, labelled.
+    c.setFont("Helvetica", 5)
+    for i in range(0, int(content_w) + 1, 10):
+        tall = i % 20 == 0
+        c.setLineWidth(0.6 if tall else 0.3)
+        c.line(X(i), Y(0), X(i), Y(3.5 if tall else 1.8))
+        if tall:
+            c.drawString(X(i + 0.4), Y(3.8), str(i))
+
+    # Y ruler: a tick every 2 mm up the left edge, labelled every 6 mm.
+    for j in range(0, int(content_h) + 1, 2):
+        tall = j % 6 == 0
+        c.setLineWidth(0.6 if tall else 0.3)
+        c.line(X(0), Y(j), X(2.5 if tall else 1.4), Y(j))
+        if tall:
+            c.drawString(X(2.8), Y(j + 0.3), str(j))
+
+    # 10 x 10 mm reference square, for an independent scale check.
+    c.setLineWidth(0.6)
+    c.rect(X(30), Y(4), 10 * mm, 10 * mm)
+    c.setFont("Helvetica-Bold", 4)
+    c.drawString(X(30.6), Y(8.4), "10x10")
+    c.drawString(X(30.6), Y(6.0), "mm")
+
+    # Explanation printed on the label itself.
+    c.setFont("Helvetica-Bold", 5)
+    c.drawString(X(44), Y(15.4), "MEASURE:")
+    c.setFont("Helvetica", 4)
+    c.drawString(X(44), Y(13.4), "tick 0 to 60")
+    c.drawString(X(44), Y(11.6), "should be 60 mm")
+    c.drawString(X(44), Y(9.8), "square = 10 mm")
+    c.drawString(X(44), Y(8.0), "frame =")
+    c.drawString(X(44), Y(6.4), f"{content_w:.0f} x {content_h:.0f} mm")
+    c.drawString(X(44), Y(4.8), "tape = 24 mm")
+
+    c.showPage()
+    c.save()
+    return path
+
+
+def main() -> int:
+    cfg = load_config()
+
+    # Use the printer's real printable area for this measurement.
+    area = query_print_area(PRINTER)
+    if area:
+        print(f"Printable area: {area.printable_width_mm:.2f} x "
+              f"{area.printable_height_mm:.2f} mm")
+        cfg.media_width_mm = round(area.media_width_mm, 2)
+        cfg.media_height_mm = round(area.media_height_mm, 2)
+        cfg.page_width_mm = round(area.printable_width_mm - 0.1, 2)
+        cfg.page_height_mm = round(area.printable_height_mm - 0.1, 2)
+
+    os.makedirs("pdf_backup", exist_ok=True)
+    out = os.path.join("pdf_backup", "measure_scale.pdf")
+    build_measure_pdf(cfg, out)
+
+    print(f"Content bounds : {cfg.page_width_mm:.2f} x {cfg.page_height_mm:.2f} mm")
+    print(f"PDF page       : {cfg.page_size_mm[0]:.2f} x {cfg.page_size_mm[1]:.2f} mm")
+    print(f"Origin         : {cfg.origin_mm}")
+    print(f"Written        : {out}")
+
+    if "--no-print" in sys.argv:
+        print("(--no-print: not sending to printer)")
+        return 0
+
+    from print_label import print_to_printer
+
+    settings = "noscale,paperkind=261"
+    print(f"\nPrinting with -print-settings '{settings}' ...")
+    ok = print_to_printer(PRINTER, out, settings=settings)
+    print(f"Result: {'SENT' if ok else 'FAILED'}")
+    return 0 if ok else 1
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())