fix: Wonder Ink prints without crashing, and prints worksheets at all

Little Waders, 0.2.2: SIGSEGV in QPrinter::resolution() every time a
teacher confirmed a print job. QWebEngineView.print() keeps the raw
QPrinter pointer and returns; Qt's didPrintPage() reads
printer->resolution() once Chromium has rendered the page, and by then
PyQt had deleted the printer, which print_view() held only as a local.
Reproduced in the lab with the 0.2.2 code, same backtrace, no job.

Keeping the printer alive fixed the crash and was measured, and Qt's
path was still not a print path: a worksheet PDF tab printed as one
blank page, a lesson went as 24.6 MB of 300 dpi pictures with no text,
and a queue refusing jobs was reported as printed.

Print is now: make a PDF (a worksheet already is one; a lesson page is
printToPdf'd onto the printer's own paper; an inline PDF is downloaded
and opened as a worksheet), show it in a preview with printer, pages,
copies and colour, and hand it to CUPS with lp — Chrome's route in the
same rooms. Nothing asynchronous holds a printer. Black and white uses
the driver's ColorModel=Grayscale, because Elmer's generic PCL 6 driver
ignores print-color-mode.

An exception escaping any slot no longer aborts Wonder Ink: PyQt6's
default is to kill the process, and it is now logged instead.

tests/test-classroom-printing.sh: 50 checks. tools/lab/wonderink-print-
check: 39 checks over 13 scenarios in the lab, against a queue built
from Elmer's PPD, judged by what CUPS received. Not yet on paper.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

tests/test-deployment-support.sh

@@ -342,8 +342,11 @@ check("local documents may not read other local documents",
       "LocalContentCanAccessFileUrls, False" in wonderink)
 check("nor reach the network",
       "LocalContentCanAccessRemoteUrls, False" in wonderink)
-check("there is no file chooser behind the print dialog",
-      "PrintDialogOption.PrintToFile, False" in wonderink)
+# Qt's print dialog has a Print to File path with a "..." chooser behind
+# it. Wonder Ink no longer uses that dialog: its preview offers CUPS
+# printers and nothing else, and no file dialog exists anywhere in it.
+check("there is no file chooser behind printing",
+      "QFileDialog" not in wonderink and "QPrintDialog" not in wonderink)
 check("nothing downloaded is executed",
       "subprocess" not in wonderink.split("def notify")[0]
       and "QDesktopServices" not in wonderink
@@ -374,8 +377,12 @@ check("the Present-view autoplay fix is still there",
       "PlaybackRequiresUserGesture, False" in wonderink)
 check("fullscreen still returns to a maximised window",
       "WindowFullScreen" in wonderink)
+# One text box exists, and it is the print preview's page range. Anywhere
+# else a text box in this window is an address bar.
+preview = wonderink[wonderink.index("class PrintPreview"):wonderink.index("\ndef notify")]
 check("still no new-tab button or address bar",
-      "setCornerWidget" not in wonderink and "QLineEdit" not in wonderink)
+      "setCornerWidget" not in wonderink
+      and wonderink.count("QLineEdit(") == 1 and "QLineEdit(" in preview)
 
 print()
 print("7b. the disc player is decided before a session starts")