perf(bench): introduce standardized 25-metric CAD and UI benchmark suite

- Add comprehensive performance benchmark harness in benches/performance_benchmarks.rs
  configured with harness = false in Cargo.toml (runs via cargo bench in --release,
  isolated from cargo test).
- Benchmark coverage across 25 distinct CAD & UI operations:
  * Entity Ingestion, GPU Wire Partitioning, Analytical & Wide/Tapered Arc Tessellation
  * 100x Zoom Navigation, Spatial InteractionIndex, Multi-mode Hit-Testing, OSnap Tracking
  * 2D Parametric Dogleg Constraint Solving, DXF Import/Export Throughput
  * UI Ribbon View Construction, Viewport Grid Projection, Grid Cache Evaluation
  * Themed SVG Icon Lookup Caching, Cold Extents AABB Calculation
  * Batch Entity Transformation, Draworder Depth Map Full/Patch, Delta-Undo Recording
- Expose internal calculation hooks with #[doc(hidden)] pub to prevent API leakage.
- Remove 644 lines of legacy, scattered ad-hoc #[test] #[ignore] benchmarks across src/.
- Add developer and regression documentation in benches/README.md.

src/ui/ribbon/mod.rs

@@ -1610,76 +1610,5 @@ mod tests {
         assert!(ribbon.escape_extension());
         assert_eq!(ribbon.open_dropdown, None);
     }
-
-    /// Reproducible element-construction benchmark for the ribbon view. Run with:
-    /// `cargo test --lib --release -- --ignored --nocapture bench_ribbon_view_construction`
-    ///
-    /// Times `Ribbon::view()` element construction — the dominant cost in the
-    /// cheap (non-render) part of a ribbon frame, and the thing Mission #4
-    /// reworked. `#[ignore]`d so normal runs stay silent; state is populated so
-    /// Auto-mode panels actually have four densities to build.
-    #[test]
-    #[ignore]
-    fn bench_ribbon_view_construction() {
-        use std::time::Instant;
-        use super::*;
-
-        let mut ribbon = Ribbon::new();
-        ribbon.set_styles(
-            vec![
-                "Standard".to_string(),
-                "Title".to_string(),
-                "Annotative".to_string(),
-            ],
-            "Standard",
-            vec!["Standard".to_string()],
-            "Standard",
-            vec!["Standard".to_string()],
-            "Standard",
-            vec!["Standard".to_string()],
-            "Standard",
-        );
-        ribbon.set_layers(
-            vec![
-                LayerInfo {
-                    name: "0".to_string(),
-                    color: Color::TRANSPARENT,
-                    visible: true,
-                    frozen: false,
-                    locked: false,
-                },
-                LayerInfo {
-                    name: "DRAWING".to_string(),
-                    color: Color::TRANSPARENT,
-                    visible: true,
-                    frozen: false,
-                    locked: false,
-                },
-            ],
-            "0",
-        );
-        ribbon.set_available_linetypes(vec![
-            LinetypeItem {
-                name: "Continuous".to_string(),
-                art: String::new(),
-            },
-            LinetypeItem {
-                name: "DASHED".to_string(),
-                art: String::new(),
-            },
-        ]);
-
-        let n = 200u32;
-        // Warm-up for allocator/tree-slot settling before timing begins.
-        let _ = ribbon.view(false, false, 0, 0, false);
-        let start = Instant::now();
-        for _ in 0..n {
-            let _ = ribbon.view(false, false, 0, 0, false);
-        }
-        let per_frame = start.elapsed() / n;
-        println!(
-            "bench_ribbon_view_construction: {per_frame:?} per `Ribbon::view()` \
-             element build (n = {n}, release measurement recommended)"
-        );
-    }
 }
+