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.

assets/icons/mt_strike.svg

@@ -0,0 +1,4 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" width="24" height="24" fill="none" stroke="#e0e0e0" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
+  <path d="M8 6 v4 a4 4 0 0 0 8 0 v-4"/>
+  <line x1="5" y1="13" x2="19" y2="13"/>
+</svg>