Add a Toolbars settings page: icon size, text with icons, lock

A new page in Configurer QElectroTech, "Barres d'outils", sets for
every window (folio editor, element editor, title block editor):
- the icon size: default, 16, 24, 32 or 48 px
- the buttons: icon only, text beside the icon, or text under it
- locking the toolbars so they can't be dragged out of place

OK applies it to the open windows at once. The defaults are Qt's
own, and a default value removes its key, so nothing changes for
anyone who never opens the page. A toolbar inside a panel is left
alone; only the window's own toolbars are locked.

New test tst_toolbarsettings: defaults change nothing, saved values
reach every toolbar of an open window, back to defaults removes the
keys.

Third stage of discussion #1319.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

cmake/qet_compilation_vars.cmake

@@ -301,6 +301,8 @@ set(QET_SRC_FILES
   ${QET_DIR}/sources/shortcutmanager.h
   ${QET_DIR}/sources/shortcutbarsettings.cpp
   ${QET_DIR}/sources/shortcutbarsettings.h
+  ${QET_DIR}/sources/toolbarsettings.cpp
+  ${QET_DIR}/sources/toolbarsettings.h
   ${QET_DIR}/sources/diagramcontexttoolbar.cpp
   ${QET_DIR}/sources/diagramcontexttoolbar.h
   ${QET_DIR}/sources/diagramgestureoverlay.cpp
@@ -854,6 +856,8 @@ set(QET_SRC_FILES
   ${QET_DIR}/sources/ui/configpage/shortcutsconfigpage.h
   ${QET_DIR}/sources/ui/configpage/shortcutbarconfigpage.cpp
   ${QET_DIR}/sources/ui/configpage/shortcutbarconfigpage.h
+  ${QET_DIR}/sources/ui/configpage/toolbarsconfigpage.cpp
+  ${QET_DIR}/sources/ui/configpage/toolbarsconfigpage.h
 
   ${QET_DIR}/sources/undocommand/addelementtextcommand.cpp
   ${QET_DIR}/sources/undocommand/addelementtextcommand.h