PDFSHXTEXT: recognise SHX text geometry as MText

Adds PDFSHXTEXT with the PDF Text Recognition Settings dialog, its
command-line form, the PDFSHXLAYER / PDFSHXBESTFONT / PDFSHXTEXTSETTINGS
variables and the profile settings they are kept in.

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

src/app/mod.rs

@@ -595,6 +595,7 @@ pub(super) struct OpenCADStudio {
     image_adjust: Option<crate::ui::window::pdf_dialogs::ImageAdjustState>,
     /// The Edit Reference dialog (REFEDIT).
     refedit_dialog: Option<crate::ui::window::refedit_dialog::RefEditDialogState>,
+    pdf_shx_dialog: Option<crate::ui::window::pdf_shx_dialog::ShxSettingsState>,
     underlay_layers: Option<crate::ui::window::pdf_dialogs::UnderlayLayersState>,
     pdf_import_settings: Option<crate::modules::insert::pdf_import::PdfImportSettings>,
     pdf_import_file: Option<crate::ui::window::pdf_dialogs::PdfImportFileState>,
@@ -2176,6 +2177,7 @@ pub enum ModalKind {
     ViewBackground,
     ImageAdjust,
     RefEdit,
+    PdfShxSettings,
     UnderlayLayers,
     PdfImportSettings,
     PdfImportFile,
@@ -4398,6 +4400,7 @@ pub enum Message {
     FieldDialog(crate::ui::window::field_dialog::FieldDialogMsg),
     /// An edit in the Edit Reference dialog.
     RefEditDialog(crate::ui::window::refedit_dialog::RefEditDialogMsg),
+    PdfShxDialog(crate::ui::window::pdf_shx_dialog::ShxDialogMsg),
     /// A click or search in the Point Cloud Manager.
     PcManager(crate::ui::window::pc_manager::PcManagerMsg),
     Count(crate::ui::window::count_palette::CountMsg),
@@ -4614,6 +4617,7 @@ impl OpenCADStudio {
             view_background: None,
             image_adjust: None,
             refedit_dialog: None,
+            pdf_shx_dialog: None,
             underlay_layers: None,
             pdf_import_settings: None,
             pdf_import_file: None,