refactor: remove dead world_offset plumbing (RTE migration is complete)

Now that geometry reaches the GPU/CPU as absolute coordinates via the
double-single relative-to-eye path, world_offset is always [0,0,0]. Strip
the parameter that was threaded through the whole tessellation / block-
expansion / fallback / camera-decode chain and the ExpandCtx field that
carried it — ~340 references across 20 files, all subtracting zero.

- truck_tess: to_local / to_local_low / tessellate_* drop the offset arg;
  to_local is now a pure double-single split.
- tessellate: offset_to_ds → points_to_ds (pure DS split); tessellate(),
  tessellate_entity(), fallback_geometry(), solid_wire_fallback(),
  entity_aabb(), expand_insert(), expand_block_meshes(), the dimension
  helpers (vec3_local, dimension_snap_pts, …), text_support, leader,
  multileader, image_model, xclip and camera_from_view all lose the param.
- block_cache: ExpandCtx loses its world_offset field.
- Remove the now-dead offset_snap_pts and the unused set_grid_snap.

Behaviour is unchanged (the offset was zero everywhere); the compiler
verifies every call site.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/entities/text_support.rs

@@ -1702,7 +1702,6 @@ pub(crate) fn text_obb_corners_native(
 pub(crate) fn text_baseline_points(
     e: &EntityType,
     anno_scale: f32,
-    world_offset: [f64; 3],
     n_lines: usize,
 ) -> Vec<[f32; 3]> {
     let Some(corners) = text_obb_corners_native(e, anno_scale, Some(n_lines)) else {
@@ -1723,7 +1722,7 @@ pub(crate) fn text_baseline_points(
         return vec![];
     }
     let n_lines = n_lines.max(1);
-    let [ox, oy, oz] = world_offset;
+    let [ox, oy, oz] = [0.0_f64; 3];
     let cast = |p: [f64; 3]| -> [f32; 3] {
         [(p[0] - ox) as f32, (p[1] - oy) as f32, (p[2] - oz) as f32]
     };
@@ -1763,7 +1762,6 @@ pub(crate) fn text_baseline_points(
 pub(crate) fn text_greek_obb_tris(
     e: &EntityType,
     anno_scale: f32,
-    world_offset: [f64; 3],
     n_lines: usize,
 ) -> Vec<[f32; 3]> {
     let Some(corners) = text_obb_corners_native(e, anno_scale, Some(n_lines)) else {
@@ -1784,7 +1782,7 @@ pub(crate) fn text_greek_obb_tris(
         return vec![];
     }
     let n_lines = n_lines.max(1);
-    let [ox, oy, oz] = world_offset;
+    let [ox, oy, oz] = [0.0_f64; 3];
     let cast = |p: [f64; 3]| -> [f32; 3] {
         [(p[0] - ox) as f32, (p[1] - oy) as f32, (p[2] - oz) as f32]
     };