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_ptouch_pipeline.py

@@ -0,0 +1,135 @@
+"""End-to-end test of the P-touch print pipeline (no hardware required).
+
+Exercises config persistence, PDF generation, the "PDF" pseudo-printer path, and
+variable-length QR payloads, then verifies the output dimensions.
+
+IMPORTANT: this test writes to a temporary config file. It must never call
+save_config() with the default path, because that overwrites the operator's real
+settings in label_config.json.
+"""
+
+import os
+import sys
+import tempfile
+
+sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
+os.chdir(os.path.dirname(os.path.abspath(__file__)))
+
+from PIL import Image, ImageDraw
+from reportlab.lib.units import mm
+from pypdf import PdfReader
+
+import label_config
+from print_label import print_ptouch_label
+from ptouch_label import LabelConfig, PtouchLabelRenderer, code_density_warning
+
+#: Isolated directory for config written by this test.
+TEMP_DIR = tempfile.mkdtemp(prefix="ptouch_test_")
+
+
+def make_test_logo(path):
+    """Create a greyscale logo with transparency to exercise the flatten path."""
+    img = Image.new("RGBA", (400, 400), (255, 255, 255, 0))
+    draw = ImageDraw.Draw(img)
+    draw.ellipse((20, 20, 380, 380), fill=(0, 0, 0, 255))
+    draw.rectangle((150, 150, 250, 250), fill=(255, 255, 255, 255))
+    img.save(path)
+    return path
+
+
+def main():
+    base = os.path.dirname(os.path.abspath(__file__))
+    logo_path = os.path.join(TEMP_DIR, "test_logo.png")
+    make_test_logo(logo_path)
+
+    cfg = LabelConfig()
+    cfg.logo_path = logo_path
+    cfg.static_lines = ["MOTO ADV SRL", "Articol: CABLU", "Rev: 2026-09"]
+    cfg.qr_prefix = "INV-"
+    cfg.qr_suffix = "-A"
+    cfg.qr_error_correction = "M"
+
+    print("=" * 68)
+    print("1. Config persistence round-trip (in a temp dir, real config untouched)")
+    real_cfg_path = label_config.config_path()
+    real_before = open(real_cfg_path).read() if os.path.exists(real_cfg_path) else None
+
+    path = label_config.save_config(cfg, base_dir=TEMP_DIR)
+    reloaded = label_config.load_config(base_dir=TEMP_DIR)
+    print(f"   saved to      : {path}")
+    print(f"   logo preserved: {reloaded.logo_path == cfg.logo_path}")
+    print(f"   lines preserved: {reloaded.static_lines == cfg.static_lines}")
+    print(f"   prefix/suffix kept: "
+          f"{reloaded.qr_prefix == cfg.qr_prefix and reloaded.qr_suffix == cfg.qr_suffix}")
+    composed = reloaded.build_code_payload("1234")
+    print(f"   composed payload : {composed!r}  "
+          f"{'PASS' if composed == 'INV-1234-A' else 'FAIL'}")
+
+    real_after = open(real_cfg_path).read() if os.path.exists(real_cfg_path) else None
+    untouched = real_before == real_after
+    print(f"   real config untouched: {'PASS' if untouched else 'FAIL'}")
+
+    print("\n2. Unknown/corrupt keys are tolerated")
+    weird = LabelConfig.from_dict({"static_lines": "not-a-list", "bogus_key": 1})
+    print(f"   static_lines fell back: {weird.static_lines == LabelConfig().static_lines}")
+
+    print("\n3. Print pipeline via the 'PDF' pseudo-printer")
+    success, pdf_path, warning = print_ptouch_label("INV-00042", "PDF", cfg)
+    print(f"   success       : {success}")
+    print(f"   pdf           : {pdf_path}")
+    print(f"   warning       : {warning or 'none'}")
+
+    page = PdfReader(pdf_path).pages[0]
+    w_mm = float(page.mediabox.width) / mm
+    h_mm = float(page.mediabox.height) / mm
+    # With match_driver_media the page is the driver's media size and the label
+    # content is centred inside it; otherwise page size == content size.
+    want_w, want_h = cfg.page_size_mm
+    exact = abs(w_mm - want_w) < 0.01 and abs(h_mm - want_h) < 0.01
+    print(f"   page size     : {w_mm:.2f} x {h_mm:.2f} mm  {'PASS' if exact else 'FAIL'}")
+    print(f"   label content : {cfg.page_width_mm:.1f} x {cfg.page_height_mm:.1f} mm "
+          f"at origin {cfg.origin_mm}")
+
+    print("\n4. QR payload scaling with the inventory value")
+    renderer = PtouchLabelRenderer(cfg)
+    for value in ["A", "INV-00042", "MOTO-2026-0001234567"]:
+        bitmap = renderer.code_bitmap(value)
+        warn = code_density_warning(cfg, value)
+        payload = cfg.build_code_payload(value)
+        print(
+            f"   {value:<22} modules={bitmap.modules:>3} "
+            f"size={bitmap.width_mm:5.2f}mm dots/mod={bitmap.dots_per_module:.1f} "
+            f"{'OK' if not warn else 'WARN'}"
+        )
+        print(f"      payload: {payload!r}")
+        if warn:
+            print(f"      -> {warn}")
+
+    print("\n5. Oversized payload is reported, not silently misprinted")
+    huge = "X" * 300
+    warn = code_density_warning(cfg, huge)
+    print(f"   warning present: {warn is not None}")
+    print(f"   -> {warn}")
+
+    print("\n6. Preview render (what the GUI shows)")
+    preview = renderer.render_preview("INV-00042", dpi=300)
+    print(f"   preview size  : {preview.size} px @300dpi")
+    preview.save(os.path.join(base, "test_ptouch_preview.png"))
+    print(f"   saved         : test_ptouch_preview.png")
+
+    # Tidy up the test artifacts
+    for temp in (logo_path, pdf_path):
+        try:
+            if os.path.exists(temp):
+                os.remove(temp)
+        except OSError:
+            pass
+
+    print("\n" + "=" * 68)
+    passed = exact and success and untouched
+    print("RESULT:", "PASS" if passed else "FAIL")
+    return 0 if passed else 1
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())