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/plugin_host.rs

@@ -232,7 +232,7 @@ impl crate::command::CadCommand for PluginInteractiveAdapter {
         crate::plugin::guard("InteractiveCommand::prompt", || self.inner.prompt())
             .unwrap_or_default()
     }
-    fn on_point(&mut self, pt: glam::Vec3) -> crate::command::CmdResult {
+    fn on_point(&mut self, pt: glam::DVec3) -> crate::command::CmdResult {
         crate::plugin::guard("InteractiveCommand::on_point", || {
             self.inner.on_point([pt.x as f64, pt.y as f64, pt.z as f64])
         })
@@ -250,7 +250,7 @@ impl crate::command::CadCommand for PluginInteractiveAdapter {
         })
         .unwrap_or(false)
     }
-    fn on_entity_pick(&mut self, handle: Handle, pt: glam::Vec3) -> crate::command::CmdResult {
+    fn on_entity_pick(&mut self, handle: Handle, pt: glam::DVec3) -> crate::command::CmdResult {
         crate::plugin::guard("InteractiveCommand::on_object_pick", || {
             self.inner
                 .on_object_pick(handle, [pt.x as f64, pt.y as f64, pt.z as f64])