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 <noreply@anthropic.com>

src/modules/annotate/aligned_dim.rs

@@ -186,6 +186,7 @@ impl CadCommand for AlignedDimensionCommand {
         let p1 = p1.as_vec3();
         let p2 = p2.as_vec3();
         Some(WireModel {
+            dash_from_start: false,
             text_verts: Vec::new(),
             name: "dimaligned_preview".into(),
             points: vec![[p1.x, p1.y, p1.z], [p2.x, p2.y, p2.z]],
@@ -233,6 +234,7 @@ fn preview_aligned(p1: DVec3, p2: DVec3, dim_pt: DVec3) -> WireModel {
     let d1 = d1.as_vec3();
     let d2 = d2.as_vec3();
     WireModel {
+            dash_from_start: false,
             text_verts: Vec::new(),
         name: "dimaligned_preview".into(),
         points: vec![