feat(otrack): draw both vectors of an intersection lock

An OTRACK crossing is the meeting of two tracking vectors, but
`OtrackHit` carried only the one a typed distance is measured along, so
the overlay had a single guide to draw. Snapping to the crossing of two
vectors worked and looked like an unexplained point on one line.

Carry the crossed ray out of `otrack_snap` as `OtrackHit::cross`, keep it
on the app beside `otrack_active`, and let the overlay take a list of
guides rather than one. `otrack_active` still drives typed-distance
entry on its own, so distance entry is unchanged.

Fixes HakanSeven12/OpenCADStudio#1313

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TQzYZsXBwPZ5HwBaGitEUV
(cherry picked from commit 2f6caacece)

src/app/update/mod.rs

@@ -366,6 +366,7 @@ impl OpenCADStudio {
         {
             self.snapper.clear_tracking();
             self.otrack_active = None;
+            self.otrack_cross = None;
             self.otrack_kind = None;
         }
         if let Some((started, tab_id, before)) = perf_edit_before {
@@ -402,6 +403,7 @@ impl OpenCADStudio {
     pub(in crate::app) fn reset_tracking_after_point(&mut self) {
         self.snapper.clear_tracking();
         self.otrack_active = None;
+        self.otrack_cross = None;
         self.otrack_kind = None;
     }
 
@@ -3982,6 +3984,7 @@ impl OpenCADStudio {
                 if !self.snapper.otrack_enabled {
                     self.snapper.clear_tracking();
                     self.otrack_active = None;
+                    self.otrack_cross = None;
                     self.otrack_kind = None;
                 }
                 Task::none()