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/modules/draw/modify/explode.rs

@@ -26,7 +26,7 @@ use acadrust::{CadDocument, EntityType, Handle};
 
 use crate::command::{CadCommand, CmdResult};
 use crate::modules::{IconKind, ModuleEvent, ToolDef};
-use glam::Vec3;
+use glam::DVec3;
 
 // ── Ribbon definition ──────────────────────────────────────────────────────
 
@@ -447,7 +447,7 @@ impl CadCommand for ExplodeCommand {
         "EXPLODE  Select objects to explode:".into()
     }
 
-    fn on_point(&mut self, _pt: Vec3) -> CmdResult {
+    fn on_point(&mut self, _pt: DVec3) -> CmdResult {
         CmdResult::Cancel
     }
     fn on_enter(&mut self) -> CmdResult {