Add a local, per-project time-spent tracker (#576)

Adds a ProjectUsageTracker (sources/project/) that accumulates how
long a project has been the active tab, using QElapsedTimer so the
value is computed on demand rather than via polling. It's hosted on
ProjectPropertiesHandler per that class's own stated design intent
("all new properties should be managed by this class").

The accumulated time is persisted as a new <usage time_spent="N"
enabled="true|false"/> element, a sibling of <properties> in the
project XML, written/read by new QETProject::writeUsageXml()/
readUsageXml(). It rides along on the existing autosave path for
free, since writeBackup() already serializes the full project via
toXml().

QETDiagramEditor::subWindowActivated() now pauses every open
project's tracker except the one whose tab just became current, so
switching between several open projects keeps each project's tracked
time isolated.

Surfaced in the existing Project Properties "Général" page: a
"Temps passé sur ce projet" display, a "Réinitialiser" button, and
an opt-out checkbox ("uniquement enregistré localement dans ce
fichier" - this is local-only, never transmitted anywhere).

Verified beyond compiling: full CMake build, then an actual runtime
session confirming the saved XML's time_spent value, that closing
and reopening the project round-trips and resumes timing, that the
reset button works, and - the key correctness check - that with two
projects open, the inactive one's time_spent stays frozen while the
active one accumulates real elapsed time, over the same interval.

See discussion #576.

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

sources/ui/configpage/projectconfigpages.cpp

@@ -22,6 +22,7 @@
 #include "../autoNum/ui/folioautonumbering.h"
 #include "../autoNum/ui/formulaautonumberingw.h"
 #include "../autoNum/ui/selectautonumw.h"
+#include "../project/projectpropertieshandler.h"
 #include "../qeticons.h"
 #include "../qetproject.h"
 #include "../borderpropertieswidget.h"
@@ -161,6 +162,13 @@ void ProjectMainConfigPage::applyProjectConf()
 		m_project -> setProjectProperties(new_properties);
 		modified_project = true;
 	}
+
+	ProjectUsageTracker &usage_tracker = m_project -> projectPropertiesHandler().usageTracker();
+	if (usage_tracker.isEnabled() != usage_enabled_cb_ -> isChecked()) {
+		usage_tracker.setEnabled(usage_enabled_cb_ -> isChecked());
+		modified_project = true;
+	}
+
 	if (modified_project) {
 		m_project -> setModified(true);
 	}
@@ -191,6 +199,12 @@ void ProjectMainConfigPage::initWidgets()
 	project_variables_label_ -> setWordWrap(true);
 	project_variables_ = new DiagramContextWidget();
 	project_variables_ -> setContext(DiagramContext());
+
+	usage_label_ = new QLabel(tr("Temps passé sur ce projet :", "label when configuring"));
+	usage_value_ = new QLabel();
+	usage_enabled_cb_ = new QCheckBox(tr("Suivre le temps passé sur ce projet (uniquement enregistré localement dans ce fichier)", "checkbox label"));
+	usage_reset_pb_ = new QPushButton(tr("Réinitialiser", "button label"));
+	connect(usage_reset_pb_, &QPushButton::clicked, this, &ProjectMainConfigPage::resetUsageTracker);
 }
 
 /**
@@ -207,6 +221,16 @@ void ProjectMainConfigPage::initLayout()
 	main_layout0 -> addSpacing(10);
 	main_layout0 -> addWidget(project_variables_label_);
 	main_layout0 -> addWidget(project_variables_);
+	main_layout0 -> addSpacing(10);
+
+	QHBoxLayout *usage_layout0 = new QHBoxLayout();
+	usage_layout0 -> addWidget(usage_label_);
+	usage_layout0 -> addWidget(usage_value_);
+	usage_layout0 -> addStretch();
+	usage_layout0 -> addWidget(usage_reset_pb_);
+	main_layout0 -> addLayout(usage_layout0);
+	main_layout0 -> addWidget(usage_enabled_cb_);
+
 	setLayout(main_layout0);
 	this -> setMinimumWidth(680);
 
@@ -219,6 +243,27 @@ void ProjectMainConfigPage::readValuesFromProject()
 {
 	title_value_ -> setText(m_project -> title());
 	project_variables_ -> setContext(m_project -> projectProperties());
+
+	const ProjectUsageTracker &usage_tracker = m_project -> projectPropertiesHandler().usageTracker();
+	const qint64 total_seconds = usage_tracker.secondsSpent();
+	usage_value_ -> setText(tr("%1 h %2 min", "hours and minutes of time spent on a project")
+							 .arg(total_seconds / 3600)
+							 .arg((total_seconds % 3600) / 60));
+	usage_enabled_cb_ -> setChecked(usage_tracker.isEnabled());
+}
+
+/**
+	@brief ProjectMainConfigPage::resetUsageTracker
+	Reset the accumulated "time spent on this project" counter to zero and
+	refresh its displayed value. Applies immediately (not staged behind
+	OK/Cancel like the other fields on this page), since it isn't
+	destructive to any actual project content.
+*/
+void ProjectMainConfigPage::resetUsageTracker()
+{
+	m_project -> projectPropertiesHandler().usageTracker().resetSecondsSpent();
+	m_project -> setModified(true);
+	usage_value_ -> setText(tr("%1 h %2 min", "hours and minutes of time spent on a project").arg(0).arg(0));
 }
 
 /**
@@ -229,6 +274,8 @@ void ProjectMainConfigPage::adjustReadOnly()
 {
 	bool is_read_only = m_project -> isReadOnly();
 	title_value_ -> setReadOnly(is_read_only);
+	usage_enabled_cb_ -> setDisabled(is_read_only);
+	usage_reset_pb_ -> setDisabled(is_read_only);
 }
 
 //######################################################################################//

sources/ui/configpage/projectconfigpages.h

@@ -21,6 +21,8 @@
 
 class QLabel;
 class QLineEdit;
+class QCheckBox;
+class QPushButton;
 class QETProject;
 class BorderPropertiesWidget;
 class ConductorPropertiesWidget;
@@ -108,7 +110,10 @@ class ProjectMainConfigPage : public ProjectConfigPage {
 	void initLayout() override;
 	void readValuesFromProject() override;
 	void adjustReadOnly() override;
-	
+
+	private slots:
+	void resetUsageTracker();
+
 	// attributes
 	protected:
 	QLabel *title_label_;
@@ -116,6 +121,10 @@ class ProjectMainConfigPage : public ProjectConfigPage {
 	QLabel *title_information_;
 	QLabel *project_variables_label_;
 	DiagramContextWidget *project_variables_;
+	QLabel *usage_label_;
+	QLabel *usage_value_;
+	QCheckBox *usage_enabled_cb_;
+	QPushButton *usage_reset_pb_;
 };
 
 class ProjectAutoNumConfigPage : public ProjectConfigPage {