fix: open-issue sweep — drawing, plot, snap, layout and UI fixes

Fixes:
- Font prompt no longer lists bundled ltypeshp/qcadshp shape files (#1626)
- Wide polylines step at a discontinuous segment width; PEDIT marks the
  current vertex; keyword steps refresh the command preview (#1628)
- Radius-0 fillet drops the zero-length segment it left, so the corner
  fillets again (#1422)
- FILLET Trim / No trim option (#1558)
- True-colour wires plot in their own colour; colour picker stores the
  value it shows (#1621)
- Model tab keeps its page setup; "Save changes to layout" in Model (#1620)
- QNEW default template in Options > Files; .dwt in the open dialog
  (#1134, #1113)
- GRIDUNIT / GRIDMODE / PERSPECTIVE variables (#1618, #1524)
- PTYPE (#1433)
- ZOOM nX / nXP (#1465)
- CHSPACE between model and paper space through a viewport (#1428)
- Moving a dimension keeps its automatic text placement
- Shell icon; "&&" button labels (#1554)
- LINETYPE Load from a .lin file (#1588)
- XLINE / RAY hide the crosshair arms (#1437)
- Dynamic-input boxes keep clear of the crosshair and each other (#1546)
- Snap marker colour setting, dark default on light canvases
  (#1497, #1229, #1128)
- Dimension style precision as a 0.00 pattern dropdown (#1426)
- Node graph nodes left of the origin no longer clip away (#1592)
- Collapse button in the command history header (#1094)
- Freeze-in-current-viewport toggle in the ribbon layer list (#1466)
- Geometric Center object snap for closed polylines (#1369)

New strings translated in all 21 locales.

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

src/scene/convert/tessellate.rs

@@ -180,6 +180,21 @@ pub(crate) fn text_contrast_background(
 /// Split each absolute f64 source point into double-single (high, low) f32
 /// buffers in one pass — the relative-to-eye residual the GPU/CPU reconstruct
 /// to f64 precision at UTM-scale coordinates.
+/// Area centroid of a closed polyline, for the Geometric Center snap.
+fn geometric_center(entity: &EntityType) -> Option<glam::DVec3> {
+    let closed = match entity {
+        EntityType::LwPolyline(p) => p.is_closed && p.vertices.len() >= 3,
+        EntityType::Polyline2D(p) => p.is_closed() && p.vertices.len() >= 3,
+        _ => false,
+    };
+    if !closed {
+        return None;
+    }
+    let planar = crate::entities::curve::entity_curve(entity)?;
+    let center = planar.curve.enclosed_centroid()?;
+    Some(glam::DVec3::from_array(planar.plane.point_at(center)))
+}
+
 pub(crate) fn points_to_ds(
     src: impl IntoIterator<Item = [f64; 3]>,
 ) -> (Vec<[f32; 3]>, Vec<[f32; 3]>) {
@@ -1102,7 +1117,10 @@ pub fn tessellate(
             )),
             _ => convert(entity, document),
         });
-    if let Some(te) = te {
+    if let Some(mut te) = te {
+        if let Some(center) = geometric_center(entity) {
+            te.snap_pts.push((center, SnapHint::GeometricCenter));
+        }
         match te.object {
             // ── Text / MText: pre-tessellated glyph strokes ───────────────
             //