Remember last-used shape/text style for new items this session

Drawing tools on the diagram canvas always started new shapes and free
text from a fixed hardcoded default (Qt's plain QPen()/QBrush(), and
the static Preferences font) -- changing a shape's color or a text's
font had zero effect on what the next new item of that type got, even
within the same editing session.

Add LastUsedStyle: a small in-memory, session-scoped static helper
(no QSettings, no persistence across restarts -- this is a live "what
did I just use" value, not a new app-wide default). Write side hooks
capture the value right where the properties editors already apply a
change (ShapeGraphicsItemPropertiesWidget::associatedUndo(), both the
live-edit dock path and the modal editProperty() dialog path; and
IndiTextPropertiesWidget::on_m_font_pb_clicked() right after the font
dialog returns). Read side hooks apply the stored value, if any, to a
newly created item: DiagramEventAddShape::mousePressEvent for shapes,
IndependentTextItem's constructor for free text (falling back to the
existing QETApp::indiTextsItemFont() Preferences default otherwise).

Doesn't touch the element/symbol editor's own drawing tools (a
separate subsystem) or add last-used text color (no color control
exists in the text properties UI to originate it from yet).

sources/lastusedstyle.h

@@ -0,0 +1,63 @@
+/*
+	Copyright 2006-2026 The QElectroTech Team
+	This file is part of QElectroTech.
+
+	QElectroTech is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 2 of the License, or
+	(at your option) any later version.
+
+	QElectroTech is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with QElectroTech.  If not, see <http://www.gnu.org/licenses/>.
+*/
+#ifndef LAST_USED_STYLE_H
+#define LAST_USED_STYLE_H
+
+#include <QBrush>
+#include <QFont>
+#include <QPen>
+
+/**
+	@brief The LastUsedStyle class
+	Session-scoped "last used" style for new shapes and free text created
+	on the diagram canvas: whatever pen/brush/font was last applied through
+	the properties editors becomes the starting point for the next new
+	item of that type, the way most drawing tools behave.
+
+	Deliberately in-memory only, not QSettings-backed: this is a live
+	"what did I just use" value for the current editing session, not an
+	app-wide default (that's already covered by the Preferences dialog's
+	font setting, read as the fallback when nothing has been set yet).
+*/
+class LastUsedStyle
+{
+	public:
+		static bool hasShapePen();
+		static QPen shapePen();
+		static void setShapePen(const QPen &pen);
+
+		static bool hasShapeBrush();
+		static QBrush shapeBrush();
+		static void setShapeBrush(const QBrush &brush);
+
+		static bool hasTextFont();
+		static QFont textFont();
+		static void setTextFont(const QFont &font);
+
+	private:
+		LastUsedStyle() = delete;
+
+		static QPen m_shape_pen;
+		static bool m_has_shape_pen;
+		static QBrush m_shape_brush;
+		static bool m_has_shape_brush;
+		static QFont m_text_font;
+		static bool m_has_text_font;
+};
+
+#endif // LAST_USED_STYLE_H