feat(snap): OTRACK ortho lock + edge-extension tracking (#218, #219)

#218: with Ortho on and a base point the axis is now a hard lock — a lone
tracking ray can't pull the cursor off it. Only a tracking ray crossing
the ortho axis locks (the corner-finding case); otherwise the ortho
constraint applies as the fallback, so Ortho reliably locks when OTRACK
is also on.

#219: an acquired corner now contributes an alignment ray along its own
edge direction(s) (captured once at acquisition), so OTRACK follows a
segment's extension, not just the ortho/polar axes. Acquisition is also
captured on leave — a perfectly still cursor emits no move events, so
"pause on a corner, then drag" now reliably acquires it. The acquired
marker projects through the active pane's camera + rect (canvas offset
included) instead of vanishing, and the active alignment path is drawn
as a full-length dashed guide through the corner.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/update/viewport.rs

@@ -900,6 +900,7 @@ pub(super) fn on_tick(&mut self, t: Instant) -> Task<Message> {
                         let snap_world = self.tabs[i].snap_result.map(|s| s.world.as_vec3());
                         self.snapper.update_otrack_dwell(
                             snap_world,
+                            &all_wires[..],
                             view_rot,
                             eye,
                             bounds,
@@ -919,6 +920,7 @@ pub(super) fn on_tick(&mut self, t: Instant) -> Task<Message> {
                                 bounds,
                                 step,
                                 self.last_point,
+                                self.ortho_mode,
                                 ucs,
                             )
                         } else {
@@ -1803,7 +1805,7 @@ pub(super) fn on_tick(&mut self, t: Instant) -> Task<Message> {
                             };
                             let ucs = self.tabs[i].scene.viewcube_ucs_mat();
                             self.snapper
-                                .otrack_snap(raw.as_vec3(), view_rot, eye, bounds, step, self.last_point, ucs)
+                                .otrack_snap(raw.as_vec3(), view_rot, eye, bounds, step, self.last_point, self.ortho_mode, ucs)
                         } else {
                             None
                         };