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 ───────────────
             //

src/scene/dimension_assoc_chain.rs

@@ -54,7 +54,7 @@ pub(crate) fn osnap_type_for(snap: crate::snap::SnapType) -> u8 {
         S::Nearest | S::Extension => osnap::NEAR,
         S::ApparentIntersection => osnap::APPARENT_INT,
         S::Parallel => osnap::PARA,
-        S::Grid | S::ObjectPick | S::Vertex | S::EdgeMidpoint | S::FaceCenter | S::Knot | S::FacePerpendicular | S::NearestFace => {
+        S::GeometricCenter | S::Grid | S::ObjectPick | S::Vertex | S::EdgeMidpoint | S::FaceCenter | S::Knot | S::FacePerpendicular | S::NearestFace => {
             osnap::NONE
         }
     }

src/scene/mod.rs

@@ -6300,6 +6300,39 @@ impl Scene {
         Some(scale_handle)
     }
 
+    /// Scale the active viewport to `factor` paper units per model unit
+    /// (ZOOM nXP). A named scale of that factor is linked as its annotation
+    /// scale; otherwise the viewport keeps a custom scale.
+    pub fn set_viewport_scale_factor(&mut self, factor: f64) -> bool {
+        let Some(viewport) = self.explicit_viewport_handle() else {
+            return false;
+        };
+        let unit_factor = self.annotation_scale_unit_factor();
+        let named = self.document.objects.values().find_map(|object| match object {
+            ObjectType::Scale(scale)
+                if !scale.is_temporary
+                    && (scale.factor() * unit_factor - factor).abs() <= 1.0e-9 * factor.max(1.0) =>
+            {
+                Some(scale.name.clone())
+            }
+            _ => None,
+        });
+        if let Some(name) = named {
+            return self.set_viewport_scale_named_for(viewport, &name).is_some();
+        }
+        match self.document.get_entity_mut(viewport) {
+            Some(EntityType::Viewport(vp)) if !vp.status.locked && factor > 1.0e-9 => {
+                vp.custom_scale = factor;
+                vp.view_height = vp.height / factor;
+            }
+            _ => return false,
+        }
+        self.notify_viewport_changed(viewport);
+        self.resident_wire_sets.borrow_mut().clear();
+        self.bump_geometry();
+        true
+    }
+
     pub fn viewport_annotation_scale_synced(&self) -> Option<bool> {
         let viewport = self.explicit_viewport_handle()?;
         let EntityType::Viewport(vp) = self.document.get_entity(viewport)? else {

src/scene/model/wire_model.rs

@@ -4,6 +4,8 @@
 pub enum SnapHint {
     /// Geometric center of a circle, arc, or ellipse.
     Center,
+    /// Area centroid of a closed polyline.
+    GeometricCenter,
     /// Point entity location.
     Node,
     /// 0 / 90 / 180 / 270 ° point on a circle/arc (within arc span).