ifcviewer: load rdb/ifc as property data source on sidecar hit

Sidecar hits skipped opening the underlying .rdb/.ifc, so ifcFile() was
null and the property panel only showed cached name/type/guid. Now, after
a sidecar hit, a background thread opens <stem>.rdb (preferred) or
<stem>.ifc and hands the file to GeometryStreamer via setIfcFile(), with
a dataSourceReady signal so the UI refreshes the current selection.

Gated behind a new AppSettings::loadDataSource toggle (default on) so
users can opt into geometry-only viewing; when off, the sidecar-hit
thread is skipped and the stream-path ifc_file_ is released after
the sidecar write completes.

Also adds *.ifcview to the Add Files dialog filter so a cache can be
opened directly without its source file present.

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

src/ifcviewer/GeometryStreamer.h

@@ -53,6 +53,11 @@ public:
     void loadFile(const std::string& path, uint32_t start_object_id, uint32_t model_id, int num_threads = 0);
     void cancel();
 
+    // Adopt an externally-opened ifcopenshell::file as the data source
+    // (e.g. for the sidecar-hit path, where loadFile never runs).  The
+    // streamer must not be running geometry iteration when this is called.
+    void setIfcFile(std::unique_ptr<ifcopenshell::file> file);
+
     bool isRunning() const { return running_.load(); }
     int progress() const { return progress_.load(); }
     uint32_t lastObjectId() const { return next_object_id_; }