perf(grips): cap total selection grips at 4096

GRIPOBJLIMIT gates object count, but one dense polyline emits ~2
grips/vertex past it (~200K grips through the per-frame project + draw
path, ms-scale, no cache). Enforce a vertex budget once in
refresh_selected_grips: stable vertex-first priority, entity order
restored, handles truncated in lockstep. Below the cap selections are
byte-identical.

Tests:
- refresh_selected_grips_caps_total_grip_count: cap + handles lockstep
- refresh_selected_grips_prefers_vertex_grips_over_midpoints: vertices survive
- grip_budget_boundary_lengths: empty/cap/cap+1 edge cases

Bench (cargo bench grip, 200K-grip fixture): per-frame 6.8ms -> 0.13ms
(45-52x); select-time build 2.36ms full. A/B reference deleted.

src/app/mod.rs

@@ -44,6 +44,13 @@ mod visibility;
 
 pub use style_ops::StyleKind;
 
+/// Re-exported `pub` (not `pub(crate)`) so the `cargo bench` harness
+/// (`benches/`, an external crate) can measure the real grip-budget helper as
+/// `ui_grip_budget`. The `properties` / `settings` modules themselves stay
+/// private / `pub(crate)`; only these two names are reachable externally.
+pub use properties::apply_grip_budget;
+pub use settings::MAX_SELECTED_GRIPS;
+
 use document::DocumentTab;
 
 use crate::modules::ModuleEvent;