feat(polyline): Polyline2D width band + tube, and block-instance shader bands

Extends the wide-polyline shader band to the two cases the first pass left on
the hatch pipeline.

Polyline2D:
- A flat wide Polyline2D now draws its band from the centre-line wire
  (`world_width`), same as LwPolyline (`polyline_band_width` handles both).
- A thickened wide Polyline2D extrudes a solid 3-D tube. `thick_wide_band`'s
  body moves to a shared `common::thick_band_tube(origin, fills, thickness,
  normal, to_wcs)`; LwPolyline delegates to it and Polyline2D calls it from
  its thickness path. Tube edges read black for both kinds.
- The model-space wide-band hatch loop is deleted (both kinds now wire/tube).

Blocks:
- Block-internal wide polylines draw the shader band too. `LocalWire` carries
  `world_width`; `emit_wire` scales it by the insert transform (average of the
  X/Y axis image lengths) so the band tracks a scaled insert, and the scaled
  width joins the batch `style_key`. `push_block_wide_fills` (the block hatch
  band) is removed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/entities/lwpolyline.rs

@@ -115,57 +115,8 @@ fn thick_wide_band(
     tangents: Vec<TangentGeom>,
 ) -> TruckEntity {
     let (origin, fills) = wide_fills(pl);
-    let (nx, ny, nz) = normal;
-    let t = thickness;
-    let off = |p: [f64; 3]| -> [f64; 3] { [p[0] + t * nx, p[1] + t * ny, p[2] + t * nz] };
-    let push_seg = |lines: &mut Vec<[f64; 3]>, a: [f64; 3], b: [f64; 3]| {
-        lines.push(a);
-        lines.push(b);
-        lines.push([f64::NAN; 3]);
-    };
-
-    let mut lines: Vec<[f64; 3]> = Vec::new();
-    // Shaded surfaces: the vertical walls plus the top cap. The flat bottom cap
-    // is already drawn by the wide-fill hatch path, so it is not repeated here.
-    let mut fill_tris: Vec<[f64; 3]> = Vec::new();
-    for poly in &fills {
-        let n = poly.len();
-        if n < 4 {
-            continue;
-        }
-        // `polyline_segment_fill` returns the band loop as the outer boundary
-        // forward then the inner boundary back, so the two transition edges
-        // (half-1 → half and n-1 → 0) are the radial segment ends.
-        let half = n / 2;
-        let bot: Vec<[f64; 3]> = poly
-            .iter()
-            .map(|&[x, y]| {
-                let (wx, wy, wz) = to_wcs(origin[0] + x as f64, origin[1] + y as f64);
-                [wx, wy, wz]
-            })
-            .collect();
-        let top: Vec<[f64; 3]> = bot.iter().map(|&p| off(p)).collect();
-        for k in 0..n {
-            // Vertical at every boundary point.
-            push_seg(&mut lines, bot[k], top[k]);
-            // Skip the two radial cap edges — they stay inside the band.
-            if k == half - 1 || k == n - 1 {
-                continue;
-            }
-            let kn = (k + 1) % n;
-            push_seg(&mut lines, bot[k], bot[kn]); // bottom boundary
-            push_seg(&mut lines, top[k], top[kn]); // top boundary
-            // Wall quad (two triangles).
-            fill_tris.extend_from_slice(&[
-                bot[k], bot[kn], top[kn], bot[k], top[kn], top[k],
-            ]);
-        }
-        // Bottom + top caps — the band ring triangulated at each plane. The
-        // bottom cap is a real 3-D surface (with depth) so the walls occlude it
-        // correctly; the flat 2-D band fill is skipped for thickened polylines.
-        fill_tris.extend(crate::entities::mesh::triangulate_planar(&bot));
-        fill_tris.extend(crate::entities::mesh::triangulate_planar(&top));
-    }
+    let (fill_tris, lines) =
+        crate::entities::common::thick_band_tube(origin, &fills, thickness, normal, to_wcs);
 
     TruckEntity {
         pick_tris: fill_tris.clone(),