feat(measuregeom): Quick mode measures around the cursor

MEASUREGEOM gains a Quick option. As the cursor moves, the nearest
drawn geometry along the working plane's X and Y lines through it is
measured live: cyan measurement lines and a Horizontal/Vertical readout
by the cursor. A click prints the current readout and keeps measuring;
Enter ends the command. The rays go through the scene's interaction
index, so large drawings stay responsive.

A structure-pick command whose miss message is empty now gets the click
as a plain point instead of an error.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/scene/mod.rs

@@ -10150,6 +10150,20 @@ impl Scene {
         }
     }
 
+    /// Wires of the space being edited that may cross a world-XY box: the
+    /// indexed broad phase in model space, every wire elsewhere.
+    pub fn interaction_candidates_xy(
+        &self,
+        aabb: [f64; 4],
+    ) -> crate::scene::pick::interaction_index::InteractionCandidates {
+        let wires = self.hit_test_wires();
+        if self.current_layout != "Model" || !self.interaction_index_worthwhile(&wires) {
+            return crate::scene::pick::interaction_index::InteractionCandidates::all(wires)
+                .materialize_stubs();
+        }
+        self.indexed_interaction_candidates_xy(wires, aabb, false, false)
+    }
+
     /// Small simple sets are cheaper to scan. Either many wires or substantial
     /// sub-geometry (one giant polyline/text batch/mesh) enables the index.
     const INTERACTION_INDEX_MIN_WIRES: usize = 4_000;