Design tab: Text dialog with font, height and live outline; offer header

- Text opens a dialog instead of a bare text entry: any installed font
  (bold, italic), the height in mm, and a live outline of exactly what
  will be inserted with its size. Enter inserts, Esc cancels; the last
  font and height are remembered. text_to_regions gains an overload
  taking a loaded font.
- The offer menu opens with a greyed title naming what the rows act on
  ("Flat face 4 of Body 2", "Sketch line", "Nothing selected").

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QK4VgguuCAk2hZLWgcjJb9

docs/CAD/design_tab.md

@@ -60,6 +60,9 @@ pointing at things stays quiet.
 The offer also opens by itself the moment you press Sketch on a face or plane, showing the
 sketch tools — the app hands you the tools directly.
 
+The first line names what the rows act on — *"Flat face 4 of Body 2"*, *"Sketch line"*,
+*"Nothing selected"* — so the menu is readable even when the selection is not under the cursor.
+
 **Eight families, always in this fixed order:** Create, Add material, Remove, Dress-up,
 Repeat, Transform, Reference, Modify.
 
@@ -302,6 +305,10 @@ variable and the whole model follows.
 
 ## Import and export
 
+**Text** asks for the words, the font (any installed font, bold, italic) and the height, and
+shows the outline that will be inserted with its size in millimetres before anything is added.
+The last font and height are remembered.
+
 **Import STEP** brings in a real B-rep solid, not a mesh: its faces and edges can be filleted,
 shelled and cut like anything modelled here.