fix(grips): compute grip positions in f64 so they sit on the wire

Grip markers drew visibly offset from the entity on large-coordinate
(UTM-scale) drawings: every Grippable impl cast the f64 entity coordinates
to f32 BEFORE the world-offset subtraction, and at 1e7 magnitude an f32
holds ~0.9 drawing units of rounding error. The wires subtract the offset
in f64 first (precision-preserving), so the grips landed up to ~1 unit
away from the geometry they belong to.

GripDef.world is now DVec3: producers fill it straight from the f64
entity data, refresh_selected_grips subtracts the world offset in f64,
and only the small offset-local result is cast to f32 for screen-space
projection (grips_to_screen / find_hit_grip) and drag state.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/entities/solid.rs

@@ -18,6 +18,10 @@ fn v3(v: &acadrust::types::Vector3) -> [f64; 3] {
     [v.x, v.y, v.z]
 }
 
+fn dvec3(v: &acadrust::types::Vector3) -> glam::DVec3 {
+    glam::DVec3::new(v.x, v.y, v.z)
+}
+
 fn v3f32(v: &acadrust::types::Vector3) -> [f32; 3] {
     [v.x as f32, v.y as f32, v.z as f32]
 }
@@ -66,10 +70,10 @@ impl TruckConvertible for Solid {
 impl Grippable for Solid {
     fn grips(&self) -> Vec<GripDef> {
         vec![
-            square_grip(0, Vec3::from(v3f32(&self.first_corner))),
-            square_grip(1, Vec3::from(v3f32(&self.second_corner))),
-            square_grip(2, Vec3::from(v3f32(&self.third_corner))),
-            square_grip(3, Vec3::from(v3f32(&self.fourth_corner))),
+            square_grip(0, dvec3(&self.first_corner)),
+            square_grip(1, dvec3(&self.second_corner)),
+            square_grip(2, dvec3(&self.third_corner)),
+            square_grip(3, dvec3(&self.fourth_corner)),
         ]
     }