fix(view): Zoom Extents and All frame a drawing placed at survey coordinates (#1829)

A block whose content is only 3D solids leaves a marker wire carrying
its insertion snap, and that point counted as drawing extent: a
georeferenced block inserted at the origin made ZOOM E frame the
origin and the model together, 860 km wide. Extents now skip those
markers; the solids count through their meshes. The marker's snap also
took the insertion point straight from the OCS, so a mirrored insert's
snap sat on the far side of the origin.

ZOOM All fitted the limits alone. In a 3D view it is now Zoom
Extents, and in plan it frames the limits together with the extents.

Instanced solids summed their rotated point and translation in f32
before meeting the eye, which cost up to half a metre at survey
coordinates; the large terms now cancel first.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/shaders/mesh.wgsl

@@ -153,17 +153,27 @@ fn relative_position(
     position_low: vec3<f32>,
     instance: MeshInstance,
 ) -> vec3<f32> {
-    let world_high = vec3<f32>(
-        dot(instance.model_row_0.xyz, position) + instance.model_row_0.w,
-        dot(instance.model_row_1.xyz, position) + instance.model_row_1.w,
-        dot(instance.model_row_2.xyz, position) + instance.model_row_2.w,
+    // Large terms cancel before small ones join: the translation against the
+    // eye first, then the rotated point, so neither a survey-placed instance
+    // nor a block drawn at survey coordinates loses its low bits to an f32
+    // sum (it cost up to half a metre).
+    let translation_high = vec3<f32>(
+        instance.model_row_0.w,
+        instance.model_row_1.w,
+        instance.model_row_2.w,
     );
-    let world_low = vec3<f32>(
+    let rotated_high = vec3<f32>(
+        dot(instance.model_row_0.xyz, position),
+        dot(instance.model_row_1.xyz, position),
+        dot(instance.model_row_2.xyz, position),
+    );
+    let rotated_low = vec3<f32>(
         dot(instance.model_row_0.xyz, position_low),
         dot(instance.model_row_1.xyz, position_low),
         dot(instance.model_row_2.xyz, position_low),
-    ) + instance.translation_low.xyz;
-    return (world_high - u.eye_high) + (world_low - u.eye_low);
+    );
+    return ((translation_high - u.eye_high) + rotated_high)
+        + (rotated_low + instance.translation_low.xyz - u.eye_low);
 }
 
 fn mesh_instance(input: InstanceIn) -> MeshInstance {