feat(f64): command layer compiles on DVec3

Whole command/snap/grip/cursor chain now builds on f64 DVec3 end to end,
so picked points, snaps and grip drags stay precise at UTM-scale
coordinates instead of quantizing to ~0.5 m through f32.

- All ~80 command files migrated: draw (line/circle/arc/ellipse/shapes
  in full f64; others via point methods), modify, annotate, insert, view,
  inquiry, layers, groups, clipboard, layout.
- Entity apply_grip impls updated for GripApply::{Absolute,Translate}(DVec3).
- Construction sites (EntityTransform/CmdResult/DynAnchor) emit DVec3;
  wire-preview boundaries cast to f32 only at the GPU edge.
- Modify/annotate commands keep internal Vec3 geometry where precision is
  non-critical, casting at the DVec3 boundary; key draw commands store f64.

Builds clean (no warnings). Visual verification of crosshair/snap/grip at
extreme UTM zoom pending.

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

src/app/automation.rs

@@ -422,7 +422,7 @@ impl OpenCADStudio {
                 if let Some(r) = self.tabs[i]
                     .active_cmd
                     .as_mut()
-                    .map(|c| c.on_entity_pick(handle, pt))
+                    .map(|c| c.on_entity_pick(handle, pt.as_dvec3()))
                 {
                     let _ = self.apply_cmd_result(r);
                 }
@@ -436,7 +436,7 @@ impl OpenCADStudio {
                 }
             }
             self.last_point = Some(pt);
-            if let Some(r) = self.tabs[i].active_cmd.as_mut().map(|c| c.on_point(pt)) {
+            if let Some(r) = self.tabs[i].active_cmd.as_mut().map(|c| c.on_point(pt.as_dvec3())) {
                 let _ = self.apply_cmd_result(r);
             }
         } else if let Some(r) = self.tabs[i]