Make auto_num_locked/potential_isolating case-insensitive

Reviving the still-relevant part of #785, closed 2026-09-10 purely to
clear a review backlog, not on merit. Investigated fresh against
current master -- one of the original PR's three targets turned out
to already be fixed independently: element_nomenclature_view's SQL
predicate for exclude_from_bom already does
"COALESCE(LOWER(TRIM(ei.exclude_from_bom)), '') NOT IN ('true', '1',
'yes', 'on')" (projectDataBase::createElementNomenclatureView()).

auto_num_locked and potential_isolating had no equivalent: five call
sites across terminal.cpp, terminalnumberingdialog.cpp and
elementinfowidget.cpp compared the raw stored string against the
literal "true" with QString::operator==, silently treating "True",
"TRUE", a trailing space, or any value written by something other
than this app's own checkbox as off -- with no error and no visible
difference from the checkbox being genuinely unticked.

Added QET::infoFlagIsTrue(), matching the same accepted spellings
("true"/"1"/"yes"/"on", case-insensitive, trimmed) the SQL predicate
already uses, and switched all five call sites to it.

Verified the exact comparison logic in isolation, outside any QET
build: 15 cases including "True", "TRUE", padded whitespace, "1",
"yes", "on", and their false counterparts -- all correctly
discriminated. Qt 6.10.2, ctest 13/13.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

sources/qetgraphicsitem/terminal.cpp

@@ -16,6 +16,7 @@
 	along with QElectroTech.  If not, see <http://www.gnu.org/licenses/>.
 */
 #include "../qetgraphicsitem/terminal.h"
+#include "../qet.h"
 #include "../qetproject.h"
 #include "../conductorautonumerotation.h"
 #include "../diagram.h"
@@ -986,7 +987,7 @@ QList<Terminal *> relatedPotentialTerminal (
 	else if (terminal -> parentElement() -> linkType() & Element::Terminale)
 	{
 		// English: Check if the user activated the potential isolation checkbox for this terminal
-		if (terminal->parentElement()->elementInformations().value(QStringLiteral("potential_isolating")).toString() == QLatin1String("true")) {
+		if (QET::infoFlagIsTrue(terminal->parentElement()->elementInformations().value(QStringLiteral("potential_isolating")).toString())) {
 			// English: Potential is isolated. Return an empty list so it does not propagate to the other side.
 			return QList<Terminal *>();
 		}