ifcviewer: promote runtime perf knobs, drop always-on settings

Promotes five env-var-driven knobs to AppSettings + the settings dialog
(min pixel radius, motion min pixel radius, LOD1 pixel threshold, HiZ
resolution, HiZ on/off).  Defaults: motion min pixel radius is now 10
(was 0/disabled) and IFC_HIZ_MOTION is on by default — the strict
view-projection gate reverts via env var =0 when chasing HiZ
correctness bugs.  ViewportWindow connects each *Changed signal so
changes invalidate cached cull state and take effect on the next
frame.

Removes "Load Property Data Source" and "Apply Coordinate Operation"
from the settings dialog: both are now hardcoded on.  The basic-info
property fallback (used when there's no live IFC source for an object,
e.g. .ifcview without a sibling) now triggers organically when
ElementRegistry::findEntity returns null instead of being gated on a
user toggle.  Federation::guessFederatedFalseOrigin lost its
apply_coordinate_operation parameter and now uses
georef.has_coordinate_operation directly.

src/ifcviewer/settings.rst documents the remaining diagnostic env vars
(IFC_HIZ_MOTION, IFC_CULL_THREADS, IFC_SKIP_MDI, IFC_MAX_SUBDRAWS,
IFC_FPS_HITCH_MS, IFC_SUBDRAW_DIAG, IFC_LOD_*) plus a cross-walk from
the old promoted-knob env-var names to their new QSettings keys.

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

src/ifcviewer/Federation.cpp

@@ -140,12 +140,10 @@ ModelGeoref computeModelGeoref(ifcopenshell::file* ifc_file) {
 FederatedFalseOrigin
 guessFederatedFalseOrigin(const Eigen::Matrix4d& first_placement_meters,
                           const ModelGeoref& georef,
-                          const FederationConfig& fed_cfg,
-                          bool apply_coordinate_operation) {
+                          const FederationConfig& fed_cfg) {
     Eigen::Vector3d t_m = first_placement_meters.block<3, 1>(0, 3);
 
-    const bool use_coord_op =
-        apply_coordinate_operation && georef.has_coordinate_operation;
+    const bool use_coord_op = georef.has_coordinate_operation;
     if (use_coord_op) {
         const Eigen::Vector4d th(t_m.x(), t_m.y(), t_m.z(), 1.0);
         t_m = (georef.coordinate_operation_meters * th).head<3>();