ifcviewer: auto-guess FederatedFalseOrigin on first model added

When the user adds a model into a fresh, untitled federation that still
has the default (0,0,0, no rotation) FederatedFalseOrigin, derive an
origin from the first instance's placement_transformation (lifted
through CoordinateOperation when enabled) and the helmert grid-north
baked into ModelGeoref::coordinate_operation_meters.  Multi-file batches
naturally settle: whichever load finishes first anchors the federation,
the rest see a non-default origin and skip.  Saved .ifcfeds keep their
authoritative origin.

Adds Placement.{h,cpp} (port of util/placement.py — a2p,
get_axis2placement, get_local_placement) so Geolocation no longer needs
its own anonymous getAxis2Placement, and xaxis2angleDeg in Geolocation
mirroring util/geolocation.xaxis2angle.

SceneLoader captures the first instance's placement_transformation from
either the sidecar's InstanceCpu[0] or the streamer's first
InstanceChunk, so the guess works on both load paths without re-reading
the IFC.

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

src/ifcviewer-full/MainWindow.h

@@ -117,6 +117,15 @@ private:
     // Push the federation-wide FederatedFalseOrigin (stage 3) matrix to
     // the viewport.  Affects every loaded model.
     void applyFederatedFalseOriginToViewport();
+
+    // For an untitled federation whose FederatedFalseOrigin is still at
+    // its default, derive a sensible origin from `mid`'s first instance
+    // placement + georef and push it via Federation.  Idempotent: a
+    // non-default origin (user-edited, already guessed by a sibling load
+    // in the same batch, or loaded from a saved .ifcfed) is left
+    // untouched, so multi-file batches naturally anchor on whichever
+    // model finishes first.
+    void maybeGuessFederatedFalseOrigin(uint32_t mid);
     QString formatElapsed(qint64 ms) const;
 
     ViewportWindow* viewport_ = nullptr;