fix(precision): keep typed coordinates exact in f64 (#311)

Typed values were quantized to the f32 grid before reaching the
entity (e.g. a length of 2000.8 committed as 2000.8020), worsening
with magnitude. The interaction point layer was all glam::Vec3 (f32).

Two-layer fix:

1. Coordinate backbone -> f64. last_point, last_cursor_world,
   dyn_anchor, dyn_ref become DVec3; UcsXform transforms, parse_coord,
   the ucs helper fns, dyn_resolve_point, the OTRACK typed-distance
   paths, command-line coordinate entry and the coordinate readout all
   compute in f64. Screen/GPU/alignment stays f32 (snap engine, render
   geometry, projection, UCS-icon/viewcube drawing) with casts only at
   those boundaries.

2. Per-command committed storage -> DVec3. on_point already received a
   DVec3, but many command impls narrowed it back to f32 (let pt =
   pt.as_vec3(); Vec<Vec3> fields) and re-widened at build, quantizing
   the committed coordinate. Migrated PLINE, SPLINE, MLINE, LENGTHEN,
   INSERT, 3D primitives, every dimension/leader/mleader, ray, revcloud,
   wipeout, attdef, table, tolerance, array center, mview, plot_window,
   plus the QDIM_PLACE handler and qdim_collect_points. Preview,
   hit-test and rubber-band paths keep f32 at the boundary.

Hatch manual boundaries are left for a follow-up: HatchModel.boundary
is structurally Arc<Vec<[f32;2]>> and needs a model-level widen.

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

src/modules/annotate/radius_dim.rs

@@ -20,8 +20,8 @@ pub fn tool() -> ToolDef {
 
 enum Step {
     CenterPoint,
-    RadiusPoint(Vec3),
-    TextPoint { center: Vec3, point: Vec3 },
+    RadiusPoint(DVec3),
+    TextPoint { center: DVec3, point: DVec3 },
 }
 
 pub struct RadiusDimensionCommand {
@@ -69,7 +69,7 @@ impl CadCommand for RadiusDimensionCommand {
         }
     }
 
-    fn on_point(&mut self, pt: DVec3) -> CmdResult { let pt = pt.as_vec3();
+    fn on_point(&mut self, pt: DVec3) -> CmdResult {
         match self.step {
             Step::CenterPoint => {
                 self.step = Step::RadiusPoint(pt);
@@ -84,7 +84,7 @@ impl CadCommand for RadiusDimensionCommand {
                 dim.base.definition_point = v3(point);
                 dim.base.text_middle_point = v3(pt);
                 dim.base.insertion_point = v3(pt);
-                dim.leader_length = point.distance(pt) as f64;
+                dim.leader_length = point.distance(pt);
                 dim.base.actual_measurement = dim.measurement();
                 dim.base.user_text = self.text_override.clone();
                 // An explicit text angle overrides the default rotation.
@@ -163,23 +163,24 @@ impl CadCommand for RadiusDimensionCommand {
         }
     }
 
-    fn on_mouse_move(&mut self, pt: DVec3) -> Option<WireModel> { let pt = pt.as_vec3();
+    fn on_mouse_move(&mut self, pt: DVec3) -> Option<WireModel> {
+        let pt = pt.as_vec3();
         match self.step {
             Step::CenterPoint => None,
-            Step::RadiusPoint(center) => Some(preview_wire(vec![center, pt])),
+            Step::RadiusPoint(center) => Some(preview_wire(vec![center.as_vec3(), pt])),
             Step::TextPoint { center, point } => Some(preview_wire(vec![
-                center,
-                point,
+                center.as_vec3(),
+                point.as_vec3(),
                 Vec3::new(f32::NAN, f32::NAN, f32::NAN),
-                point,
+                point.as_vec3(),
                 pt,
             ])),
         }
     }
 }
 
-fn v3(pt: Vec3) -> Vector3 {
-    Vector3::new(pt.x as f64, pt.y as f64, pt.z as f64)
+fn v3(pt: DVec3) -> Vector3 {
+    Vector3::new(pt.x, pt.y, pt.z)
 }
 
 fn preview_wire(points: Vec<Vec3>) -> WireModel {