Match Vertical geometric constraint behavior

1) VCONSTRAINT (and the new GCVERTICAL name) uses the axis constraint flow:
   "Select an object or [2Points] <2Points>:", 2Points mode with the
   reference's re-prompts and messages, and the same object types as
   Horizontal — line, polyline segment, text, MText, ellipse axis.
2) Object mode turns the object about its first vertex; a two-point relation
   across two objects slides the second object rigidly onto the axis.
3) Re-applying an axis constraint reports that the constraint already
   exists; Vertical follows the UCS Y direction.
4) The constraint bar draws Vertical as the reference's axis mark, with the
   point marker for a two-point relation.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

src/ui/overlay.rs

@@ -34,11 +34,16 @@ fn is_compact_coincident_glyph(label: &str) -> bool {
     matches!(label, "≡" | "∈")
 }
 
+/// Vertical's two axis-mark labels (`parametric_constraints::vertical_glyph_label`).
+fn is_vertical_glyph(label: &str) -> bool {
+    label == "│" || label == crate::scene::parametric_constraints::VERTICAL_POINTS_GLYPH
+}
+
 fn constraint_glyph_size(label: &str) -> Size {
     if is_compact_coincident_glyph(label) {
         return Size::new(COINCIDENT_GLYPH_SIZE, COINCIDENT_GLYPH_SIZE);
     }
-    if label == "G²" {
+    if label == "G²" || is_vertical_glyph(label) {
         let side = CONSTRAINT_GLYPH_SIZE + CONSTRAINT_GLYPH_PAD_Y * 2.0;
         return Size::new(side, side);
     }
@@ -94,6 +99,49 @@ fn draw_concentric_constraint_glyph(
     frame.stroke(&canvas::Path::circle(center, 2.15), stroke);
 }
 
+/// The reference bar's Vertical mark: a red datum line hatched on its left,
+/// the constrained direction beside it, plus the orange point marker for a
+/// two-point relation.
+fn draw_vertical_constraint_glyph(
+    frame: &mut canvas::Frame,
+    center: Point,
+    text: Color,
+    point_marker: bool,
+) {
+    let datum = Color::from_rgb8(214, 76, 76);
+    let datum_x = center.x - 2.5;
+    let stroke = canvas::Stroke::default().with_color(datum).with_width(1.5);
+    frame.stroke(
+        &canvas::Path::line(
+            Point::new(datum_x, center.y - 6.5),
+            Point::new(datum_x, center.y + 6.5),
+        ),
+        stroke.clone(),
+    );
+    for step in 0..3 {
+        let y = center.y - 4.5 + step as f32 * 4.0;
+        frame.stroke(
+            &canvas::Path::line(Point::new(datum_x, y), Point::new(datum_x - 4.0, y + 3.5)),
+            stroke.clone(),
+        );
+    }
+    frame.stroke(
+        &canvas::Path::line(
+            Point::new(center.x + 2.5, center.y - 6.0),
+            Point::new(center.x + 2.5, center.y + 6.0),
+        ),
+        canvas::Stroke::default().with_color(text).with_width(1.4),
+    );
+    if point_marker {
+        frame.stroke(
+            &canvas::Path::rectangle(Point::new(center.x + 4.5, center.y - 2.3), Size::new(4.6, 4.6)),
+            canvas::Stroke::default()
+                .with_color(Color::from_rgb8(224, 130, 62))
+                .with_width(1.2),
+        );
+    }
+}
+
 fn constraint_glyph_box(
     anchor: Point,
     outward: [f32; 2],
@@ -2020,6 +2068,13 @@ impl canvas::Program<Message> for SelectionCanvas {
                         draw_smooth_constraint_glyph(&mut frame, glyph_center, fg);
                     } else if label == "◎" {
                         draw_concentric_constraint_glyph(&mut frame, glyph_center, fg);
+                    } else if is_vertical_glyph(label) {
+                        draw_vertical_constraint_glyph(
+                            &mut frame,
+                            glyph_center,
+                            fg,
+                            label == crate::scene::parametric_constraints::VERTICAL_POINTS_GLYPH,
+                        );
                     } else {
                         frame.fill_text(canvas::Text {
                             content: label.clone(),