fix(render): preserve f64 precision until world_offset subtraction

Entity converters were casting WCS coordinates to f32 before the renderer
subtracted world_offset, which destroyed sub-unit precision on drawings
sitting at large coordinates (typical UTM-style CAD files). The multileader
case made it visible — glyphs warped under rotation — but every entity
that emits TruckObject::Lines/SegmentedLines/key_vertices/fill_tris was
affected.

Type changes (in src/scene/acad_to_truck.rs):
- TruckObject::Lines / SegmentedLines: Vec<[f32; 3]> → Vec<[f64; 3]>
- TruckEntity::key_vertices / fill_tris: f32 → f64

All ~17 producer files updated to keep WCS coordinates in f64 right up to
the TruckEntity boundary. The consumer in scene/tessellate.rs now performs
`(x - ox) as f32` (f64 subtract, then cast) for points, key_vertices, and
fill_tris — preserving precision near the camera origin even when the
drawing sits at million-unit coordinates.

catmull_rom_pts (multileader spline) is now f64; the scene path widens its
offset-relative f32 ctrl points to f64 around the call and narrows back at
the output.

Notes:
- Table layout still uses glam::Vec3 (f32) internally; widened to f64 only
  at the TruckEntity boundary for type compatibility. Separate cleanup to
  switch its internal math to f64 is tracked.
- snap_pts and tangent_geoms remain f32 — they are UI feedback (snap
  candidates, tangent hints) and the precision is sufficient there.

src/entities/ellipse.rs

@@ -125,9 +125,9 @@ fn to_truck(ell: &Ellipse) -> TruckEntity {
         let edge = Edge::new(&v_start, &v_end, Curve::BSplineCurve(bspline));
         let pt_start = ctrl_pts.first().unwrap();
         let pt_end = ctrl_pts.last().unwrap();
-        let key_vertices = vec![
-            [pt_start.x as f32, pt_start.y as f32, pt_start.z as f32],
-            [pt_end.x as f32, pt_end.y as f32, pt_end.z as f32],
+        let key_vertices: Vec<[f64; 3]> = vec![
+            [pt_start.x, pt_start.y, pt_start.z],
+            [pt_end.x, pt_end.y, pt_end.z],
         ];
         TruckEntity {
             object: TruckObject::Curve(edge),