bench(navigation): add viewport navigation and spatial candidate benchmarks

- Add Section 19 benchmarks covering camera pan viewport uniform updates,
  spatial hover candidate search, and viewport data assembly scaling
- Add navigation telemetry probes in src/perf.rs (active only when
  PERF=1) to track frame interval, batched input moves, and layout-draw gap

src/app/view/mod.rs

@@ -202,6 +202,7 @@ impl OpenCADStudio {
                 crate::perf_record!("[perf] view {:>7.1}ms", elapsed_ms);
             }
         }
+        crate::perf::note_view_finish();
         element
     }