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 <[email protected]>

src/ui/statusbar/mod.rs

@@ -78,12 +78,12 @@ impl StatusBar {
         // LWDISPLAY header flag — controls lineweight visibility in the viewport.
         lineweight_display: bool,
         // Live cursor position in model coordinates, for the coordinate readout.
-        cursor_world: glam::Vec3,
+        cursor_world: glam::DVec3,
         // $COORDS readout mode: 0 = static (updates only on a pick), 1 = live
         // absolute, 2 = polar (distance<angle from the last point while picking).
         coords_mode: i16,
         // The last committed point, for the static (0) and polar (2) readouts.
-        last_point: Option<glam::Vec3>,
+        last_point: Option<glam::DVec3>,
         // True while a command is prompting for a point (enables the polar readout).
         picking: bool,
         // True while clean-screen mode hides the ribbon and side panels.
@@ -385,8 +385,8 @@ impl StatusBar {
 
 // ── Coordinate readout ────────────────────────────────────────────────────
 
-fn format_coords(cursor: glam::Vec3, last: Option<glam::Vec3>, mode: i16, picking: bool) -> String {
-    let abs = |p: glam::Vec3| format!("{:.4}, {:.4}, {:.4}", p.x, p.y, p.z);
+fn format_coords(cursor: glam::DVec3, last: Option<glam::DVec3>, mode: i16, picking: bool) -> String {
+    let abs = |p: glam::DVec3| format!("{:.4}, {:.4}, {:.4}", p.x, p.y, p.z);
     match mode {
         // Static: show the last picked point; the readout freezes between picks.
         0 => abs(last.unwrap_or(cursor)),