feat: Implement in-place MText editor with formatting toolbar and live preview

- Added SVG icons for text formatting options (bold, italic, underline, overline, strike, uppercase, lowercase).
- Introduced a new `MTextEditorState` struct to manage the state of the MText editor.
- Implemented functionality to open the MText editor from the command line and edit existing MText entities.
- Added message handling for various MText editor actions (formatting, height, style, font, justification, alignment, line spacing).
- Created a dedicated preview area for MText rendering within the editor.
- Updated the command structure to support opening the MText editor and handling text input.
- Refactored existing MText command logic to integrate with the new editor.

src/app/cmd_result.rs

@@ -1496,6 +1496,16 @@ impl OpenCADStudio {
                 self.tabs[i].scene.clear_preview_wire();
                 self.restore_pre_cmd_tangent();
             }
+            CmdResult::OpenMTextEditor {
+                pos,
+                handle,
+                initial,
+                height,
+            } => {
+                self.tabs[i].active_cmd = None;
+                self.tabs[i].snap_result = None;
+                self.open_mtext_editor(pos, handle, &initial, height);
+            }
             CmdResult::DdeditEntity { handle, new_text } => {
                 let mut updated = false;
                 if let Some(entity) = self.tabs[i].scene.document.get_entity_mut(handle) {