feat: Object Snap Tracking (OTRACK / F11)

- snap/mod.rs: Snapper gains otrack_enabled, tracking_points, dwell state;
  update_otrack_dwell() acquires a snap point after DWELL_THRESHOLD=4
  consecutive moves near the same position; otrack_snap() returns an
  H/V alignment snap position; clear_tracking() resets state on command end
- overlay.rs: selection_overlay accepts ost_points + cursor_screen;
  draws light-blue dashed H/V lines from acquired points + small cross marker
- statusbar.rs: OTRACK pill (F11) added next to DYN
- view.rs: projects tracking_points to screen, passes to selection_overlay
- update.rs: calls update_otrack_dwell + otrack_snap in ViewportMove;
  overrides effective point with OST alignment when no normal snap is active
- ROADMAP.md: Object Snap Tracking marked ✅

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/view.rs

@@ -83,7 +83,23 @@ impl H7CAD {
                 None
             };
 
-            overlay::selection_overlay(sel, snap_info, grips, grid, ucs_icon)
+            // OST tracking points → screen positions.
+            let ost_points: Vec<overlay::OstTrackPoint> = if self.snapper.otrack_enabled {
+                let vp_mat = tab.scene.camera.borrow().view_proj(vp_bounds);
+                self.snapper.tracking_points.iter().map(|&wp| {
+                    let ndc = vp_mat.project_point3(wp);
+                    overlay::OstTrackPoint {
+                        screen: iced::Point::new(
+                            (ndc.x + 1.0) * 0.5 * vp_bounds.width,
+                            (1.0 - ndc.y) * 0.5 * vp_bounds.height,
+                        ),
+                    }
+                }).collect()
+            } else {
+                vec![]
+            };
+
+            overlay::selection_overlay(sel, snap_info, grips, grid, ucs_icon, ost_points, tab.last_cursor_screen)
         };
 
         let nav = container(overlay::nav_toolbar())
@@ -202,6 +218,7 @@ impl H7CAD {
                     self.polar_increment_deg,
                     self.show_grid,
                     self.dyn_input,
+                    self.snapper.otrack_enabled,
                     tab.scene.layout_names(),
                     tab.scene.current_layout.clone(),
                     self.layout_rename_state.as_ref(),
@@ -365,6 +382,9 @@ impl H7CAD {
                             keyboard::Key::Named(keyboard::key::Named::F10) => {
                                 Some(Message::TogglePolar)
                             }
+                            keyboard::Key::Named(keyboard::key::Named::F11) => {
+                                Some(Message::ToggleOTrack)
+                            }
                             keyboard::Key::Named(keyboard::key::Named::F12) => {
                                 Some(Message::ToggleDynInput)
                             }