feat(dgn-ls): dash walls from start + fix wall connector and cap identity

DET pipe walls now carry the stroke pattern (dash_from_start), which
tiles from each wall's own start vertex and skips the A-type end
alignment that was force-lighting a solid dash under the end symbol.

Two rendering fixes on top:
- Dedup the host polyline's vertices before offsetting the walls. Some
  DGN pipe polylines carry trailing duplicate end vertices; a zero-length
  segment gave offset_xy a degenerate normal, leaving that vertex
  un-offset and folding the wall down to the centre line. The two walls'
  fold segments met at the centre and drew a spurious line linking them.
- Re-key the symbol (end circle / half-ellipse) wires to the host handle
  so the whole pipe picks and selects as one entity instead of the
  symbols acting as separate phantom entities.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/modules/draw/draw/attdef.rs

@@ -160,6 +160,7 @@ impl CadCommand for AttdefCommand {
         // Show a small cross at the insertion point.
         let d = 0.15_f32;
         Some(WireModel {
+            dash_from_start: false,
             text_verts: Vec::new(),
             name: "attdef_preview".into(),
             points: vec![

src/modules/draw/draw/mline.rs

@@ -136,6 +136,7 @@ impl CadCommand for MlineCommand {
             .collect();
         pts.push([pt.x, pt.y, pt.z]);
         Some(WireModel {
+            dash_from_start: false,
             text_verts: Vec::new(),
             name: "mline_preview".into(),
             points: pts,

src/modules/draw/draw/raster_image.rs

@@ -108,6 +108,7 @@ impl CadCommand for ImageCommand {
         let p3 = [origin.x, origin.y + world_height, origin.z];
 
         Some(WireModel {
+            dash_from_start: false,
             text_verts: Vec::new(),
             name: "image_preview".into(),
             points: vec![p0, p1, p2, p3, p0],

src/modules/draw/draw/ray.rs

@@ -84,6 +84,7 @@ impl CadCommand for RayCommand {
         let dir = (pt - base).normalize_or_zero();
         let far = base + dir * DISPLAY_EXTENT;
         Some(WireModel {
+            dash_from_start: false,
             text_verts: Vec::new(),
             name: "ray_preview".into(),
             points: vec![[base.x, base.y, base.z], [far.x, far.y, far.z]],
@@ -175,6 +176,7 @@ impl CadCommand for XLineCommand {
         let far_pos = base + dir * DISPLAY_EXTENT;
         let far_neg = base - dir * DISPLAY_EXTENT;
         Some(WireModel {
+            dash_from_start: false,
             text_verts: Vec::new(),
             name: "xline_preview".into(),
             points: vec![

src/modules/draw/draw/revcloud.rs

@@ -89,6 +89,7 @@ impl CadCommand for RevCloudCommand {
             self.points[0].z as f32,
         ]);
         Some(WireModel {
+            dash_from_start: false,
             text_verts: Vec::new(),
             name: "revcloud_preview".into(),
             points: preview_pts,

src/modules/draw/draw/wipeout.rs

@@ -114,6 +114,7 @@ impl CadCommand for WipeoutCommand {
                 let min = p1.min(pt);
                 let max = p1.max(pt);
                 Some(WireModel {
+            dash_from_start: false,
             text_verts: Vec::new(),
                     name: "wipeout_preview".into(),
                     points: vec![
@@ -156,6 +157,7 @@ impl CadCommand for WipeoutCommand {
                     self.poly_pts[0].z as f32,
                 ]);
                 Some(WireModel {
+            dash_from_start: false,
             text_verts: Vec::new(),
                     name: "wipeout_poly_preview".into(),
                     points: pts,

src/modules/draw/inquiry/area.rs

@@ -69,6 +69,7 @@ impl CadCommand for AreaCommand {
         pts.push(f(pt));
         pts.push(f(self.points[0]));
         Some(WireModel {
+            dash_from_start: false,
             text_verts: Vec::new(),
             name: "area_preview".into(),
             points: pts,

src/modules/draw/inquiry/dist.rs

@@ -63,6 +63,7 @@ impl CadCommand for DistCommand {
         let p1 = self.first?;
         // The preview wire is purely visual, so f32 vertices are fine here.
         Some(WireModel {
+            dash_from_start: false,
             text_verts: Vec::new(),
             name: "dist_preview".into(),
             points: vec![

src/modules/draw/inquiry/measuregeom.rs

@@ -67,6 +67,7 @@ impl MeasureGeomCommand {
     /// Build a cyan preview wire connecting the picked points and the cursor.
     fn preview_wire(name: &str, pts: Vec<[f32; 3]>) -> WireModel {
         WireModel {
+            dash_from_start: false,
             text_verts: Vec::new(),
             name: name.to_string(),
             points: pts,

src/modules/draw/modify/trim.rs

@@ -3059,6 +3059,7 @@ fn collect_runs(pts: &[[f64; 2]], take: &dyn Fn([f64; 2]) -> bool, out: &mut Vec
 /// Build a preview wire from a NaN-break point list.
 fn preview_wire(points: Vec<[f32; 3]>, color: [f32; 4], name: &str) -> WireModel {
     WireModel {
+        dash_from_start: false,
         text_verts: Vec::new(),
         name: name.into(),
         points,