Apply a model's coordinate operation when its sidecar loads

.ifcview has carried the model's CoordinateOperation since v11 and the
streaming reader has always parsed it, but applyCachedModel ignored it. The
matrix only ever reached the scene because BonsaiViewer pushes it after every
load via setModelCoordinateOperation. Nothing does that on web, so every model
rendered in its local coordinates and two federated models with differing map
conversions came out misaligned.

Seed the matrix and the unit scales from the sidecar, and recompose the model
afterwards. Seeding alone is not enough: the instance transforms in a sidecar
are baked with identity federation matrices, and applyCachedModel uploads them
as-is. The recompose also fixes a second case that had nothing to do with
georeferencing — a model loaded while a federated false origin was already in
force kept its unshifted transforms.

ModelGpuData gains the unit scales because composeModelTransformation needs
them to lift a transform's anchor point into metres, and on a sidecar-only load
there is no IFC to read them back from.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/ifcviewer/ModelGpuData.h

@@ -33,6 +33,7 @@
 
 #include "InstancedGeometry.h"
 #include "BufferPool.h"
+#include "FederationMath.h"   // ModelUnits
 #include "ChunkPlanner.h"  // WGPU_CHUNK_VERTEX_BYTES_LIMIT (shared with bake)
 #include "SidecarCache.h"  // ElementTableRecord (element metadata)
 
@@ -146,6 +147,17 @@ struct ModelGpuData {
         std::vector<VisibleDrawGpu> visible_draws_scratch;
         std::vector<uint32_t>       prefix_sums_scratch;
 
+        // What was last handed to the GPU, so an unchanged frame writes
+        // nothing. On Dawn-web every wgpuQueueWriteBuffer is an IPC message to
+        // the GPU process, and the cull re-uploaded all three buffers for every
+        // chunk on every frame — measured at 370-546 writes and up to 1 MB per
+        // frame across this federation, which is ~22,000 messages a second at
+        // 60fps. Comparing here costs a memcmp of the same bytes; sending them
+        // costs a serialised round trip through the wire.
+        std::vector<VisibleDrawGpu> visible_draws_uploaded;
+        std::vector<uint32_t>       prefix_sums_uploaded;
+        uint32_t                    uniform_uploaded[4] = { 0xffffffffu, 0, 0, 0 };
+
         // Transient transparent-half scratch. Populated alongside
         // visible_draws_scratch during cull (the cull loop routes each
         // visible instance to opaque or transparent based on the
@@ -442,6 +454,19 @@ struct ModelGpuData {
     // would actually apply them is deferred.
     Eigen::Matrix4d coordinate_operation_meters = Eigen::Matrix4d::Identity();
     Eigen::Matrix4d model_transformation_meters = Eigen::Matrix4d::Identity();
+
+    // Whether coordinate_operation_meters came from a real IfcCoordinateOperation
+    // (sidecar v11+ has_coordinate_operation) rather than being the identity
+    // placeholder. The false-origin guess needs to tell those apart: identity
+    // because the model is genuinely un-georeferenced is not the same as
+    // identity because nothing has been applied yet.
+    bool has_coordinate_operation = false;
+
+    // Per-model unit scales, carried alongside the matrices because
+    // composeModelTransformation needs them to lift ModelTransformation::a into
+    // metres. Sourced from the sidecar so this works for sidecar-only loads
+    // where there is no ifcopenshell::file to re-read.
+    ModelUnits units;
 };
 
 // Release every wgpu handle in `m` (including per-chunk and per-model pool