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 <[email protected]>

src/scene/mod.rs

@@ -8229,7 +8229,7 @@ fn tessellate_entity(
             pattern_length: 0.0,
             pattern: [0.0; 8],
             line_weight_px: 1.0,
-            snap_pts: vec![(ip, model::wire_model::SnapHint::Insertion)],
+            snap_pts: vec![(ip.as_dvec3(), model::wire_model::SnapHint::Insertion)],
             tangent_geoms: vec![],
             key_vertices: vec![],
             aabb: WireModel::UNBOUNDED_AABB,