Merge pull request #1301: Add associative viewport dimensions

Refresh associations after complete SpaceMouse camera updates and recognize imported paper-space owners without Layout objects. Use kernel containment, intersection, perpendicular and spline tangent solving; pin cadkernel 7ce27f2 and add regressions.

src/app/commands/mod.rs

@@ -123,6 +123,9 @@ impl OpenCADStudio {
         // Reset the last committed point so the first click of the new command
         // is not constrained by ortho/polar relative to a previous command's endpoint.
         self.last_point = None;
+        // A new command collects its own points, so the previous command's
+        // accepted snaps must not leak into it.
+        self.clear_accepted_snaps();
         // Starting a command restarts the right-click cycle, so its first
         // right-click acts as Enter rather than opening the context menu.
         self.tabs[i]