fix(brush): NaN-guard EditorBrush::setPosition

applyBrush already early-outs on NaN brush position, but the stored
worldPos_ would still capture NaN and surface it to UI panels and
the brush-circle indicator (which renders a NaN ring). Reject NaN
at the setter so the editor state itself stays sane.

tools/editor/editor_brush.hpp

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <glm/glm.hpp>
+#include <cmath>
 
 namespace wowee {
 namespace editor {
@@ -31,7 +32,13 @@ public:
     void setActive(bool a) { active_ = a; }
 
     const glm::vec3& getPosition() const { return worldPos_; }
-    void setPosition(const glm::vec3& pos) { worldPos_ = pos; }
+    void setPosition(const glm::vec3& pos) {
+        // applyBrush already early-outs on NaN, but rejecting at the
+        // setter keeps the stored state itself sane — handy for UI
+        // panels that read the current brush position back.
+        if (std::isfinite(pos.x) && std::isfinite(pos.y) && std::isfinite(pos.z))
+            worldPos_ = pos;
+    }
 
     float getInfluence(float distance) const;