refactor(snap): widen snap_pts to f64 (world_offset removal P2)

WireModel/LocalWire/TruckEntity snap buffers and the producers/consumers
now carry snap candidates as DVec3 (offset_snap_pts, dimension/multileader
producers, block-cache transform, pick/xclip, snap module). Still
offset-relative, so behaviour is unchanged — this just lets the snap
transport survive the upcoming switch to absolute coordinates without an
extra f32 quantization. The snap module still resolves in f32 (as_vec3 at
entry), matching today's precision.

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

src/scene/model/wire_model.rs

@@ -57,7 +57,7 @@ pub struct WireModel {
     /// ACI color index (1-255).  0 means true-color or unknown (no CTB lookup).
     pub aci: u8,
     /// Pre-baked snap candidates (Center, Node, Quadrant, Insertion).
-    pub snap_pts: Vec<(glam::Vec3, SnapHint)>,
+    pub snap_pts: Vec<(glam::DVec3, SnapHint)>,
     /// Per-segment tangent geometry for Tangent snap.
     /// Line/Arc entities: 1 entry.  LwPolyline: 1 entry per segment.
     pub tangent_geoms: Vec<TangentGeom>,