refactor(snap): widen key_vertices to f64 (world_offset removal P4)

WireModel/LocalWire/BatchEntry key_vertices are now Vec<[f64; 3]>;
tessellation keeps them in f64 (no f32 cast at offset subtraction),
producers (dimension, leader, multileader) build them from the acadrust
f64 source, the block-cache transform keeps f64, and the face3d Face3D
quad path splits them into the double-single (high, low) pair. Consumers
(snap endpoint/midpoint, xclip) read via f32 at the leaf. Still
offset-relative (inert); endpoint/midpoint snap is no longer f32-capped.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/scene/model/wire_model.rs

@@ -64,7 +64,7 @@ pub struct WireModel {
     /// True polyline vertices used for Endpoint/Midpoint snap.
     /// Non-empty only for entities with distinct vertex positions (Line, LwPolyline).
     /// Empty for tessellated curves (Circle, Arc, Ellipse) which use snap_pts instead.
-    pub key_vertices: Vec<[f32; 3]>,
+    pub key_vertices: Vec<[f64; 3]>,
     /// World-space 2-D bounding box [min_x, min_y, max_x, max_y].
     /// Set from acadrust `bounding_box()` in `tessellate_entity()`.
     /// Preview / interim wires use `UNBOUNDED_AABB` so they are never pre-rejected