fix: restore node click/dblclick by limiting pointer capture to empty space

setPointerCapture on the SVG redirected click/dblclick events away from
node <g> elements, breaking drill-down (double-click) and potentially
click selection. Now only capture the pointer when clicking on empty SVG
space, preserving normal event flow on nodes while keeping drag-to-pan.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/components/ProcessDiagram/useZoomPan.ts

@@ -64,7 +64,11 @@ export function useZoomPan() {
       isPanning.current = true;
       didPan.current = false;
       panStart.current = { x: e.clientX - state.translateX, y: e.clientY - state.translateY };
-      (e.currentTarget as SVGSVGElement).setPointerCapture(e.pointerId);
+      // Only capture pointer on empty space — capturing on nodes would
+      // redirect click/dblclick to the SVG, breaking node interactions
+      if (!(e.target as Element).closest('[data-node-id]')) {
+        (e.currentTarget as SVGSVGElement).setPointerCapture(e.pointerId);
+      }
     },
     [state.translateX, state.translateY],
   );
@@ -85,7 +89,10 @@ export function useZoomPan() {
   const onPointerUp = useCallback(
     (e: React.PointerEvent<SVGSVGElement>) => {
       isPanning.current = false;
-      (e.currentTarget as SVGSVGElement).releasePointerCapture(e.pointerId);
+      const svg = e.currentTarget as SVGSVGElement;
+      if (svg.hasPointerCapture(e.pointerId)) {
+        svg.releasePointerCapture(e.pointerId);
+      }
     },
     [],
   );