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/mleader_cmd.rs

@@ -26,7 +26,7 @@ pub fn tool() -> ToolDef {
 }
 
 pub struct MLeaderCommand {
-    verts: Vec<Vec3>,
+    verts: Vec<DVec3>,
     ucs: Mat4,
 }
 
@@ -56,7 +56,7 @@ impl CadCommand for MLeaderCommand {
         }
     }
 
-    fn on_point(&mut self, pt: DVec3) -> CmdResult { let pt = pt.as_vec3();
+    fn on_point(&mut self, pt: DVec3) -> CmdResult {
         self.verts.push(pt);
         CmdResult::NeedPoint
     }
@@ -75,23 +75,24 @@ impl CadCommand for MLeaderCommand {
         CmdResult::Cancel
     }
 
-    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> {
         if self.verts.is_empty() {
             return None;
         }
-        let mut pts = self.verts.clone();
-        pts.push(pt);
+        // Preview / rubber-band is GPU screen-space: downcast to f32 here.
+        let mut pts: Vec<Vec3> = self.verts.iter().map(|p| p.as_vec3()).collect();
+        pts.push(pt.as_vec3());
         Some(preview_wire(&pts))
     }
 }
 
 // ── Helpers ─────────────────────────────────────────────────────────────────
 
-fn v3(p: Vec3) -> Vector3 {
-    Vector3::new(p.x as f64, p.y as f64, p.z as f64)
+fn v3(p: DVec3) -> Vector3 {
+    Vector3::new(p.x, p.y, p.z)
 }
 
-fn build_mleader(text: &str, verts: &[Vec3], ucs: Mat4) -> MultiLeader {
+fn build_mleader(text: &str, verts: &[DVec3], ucs: Mat4) -> MultiLeader {
     // Last vertex = content/text location; remaining = leader line points
     let (leader_pts, content_pt) = verts.split_at(verts.len() - 1);
     let content_pt = content_pt[0];
@@ -113,7 +114,7 @@ fn build_mleader(text: &str, verts: &[Vec3], ucs: Mat4) -> MultiLeader {
     let ux = ucs.transform_vector3(Vec3::X).normalize_or(Vec3::X);
     // Which side of the leader the text sits on, measured along the UCS X axis.
     let last_leader = leader_pts.last().copied().unwrap_or(content_pt);
-    let to_right = (content_pt - last_leader).dot(ux) >= 0.0;
+    let to_right = (content_pt - last_leader).dot(ux.as_dvec3()) >= 0.0;
     let sign = if to_right { 1.0 } else { -1.0 };
     let landing = ux * (sign as f32);