feat(RegionMap): add context menu for background clicks to show nearest system

frontend/src/components/RegionMap.tsx

@@ -482,6 +482,45 @@ export const RegionMap = ({ regionName, focusSystem, isCompact = false, isWormho
     });
   }, [viewBox]);
 
+  const handleBackgroundContextMenu = (e: React.MouseEvent) => {
+    if (!svgRef.current || systems.size === 0) return;
+    e.preventDefault();
+    e.stopPropagation();
+
+    // Convert click to SVG coordinates
+    const pt = svgRef.current.createSVGPoint();
+    pt.x = e.clientX;
+    pt.y = e.clientY;
+    const svgPoint = pt.matrixTransform(svgRef.current.getScreenCTM()!.inverse());
+    const clickX = svgPoint.x;
+    const clickY = svgPoint.y;
+
+    // Find nearest system by Euclidean distance in SVG space
+    let nearestName: string | null = null;
+    let nearestDist2 = Number.POSITIVE_INFINITY;
+    systems.forEach((sys, name) => {
+      const pos = positions[name];
+      if (!pos) return;
+      const dx = pos.x - clickX;
+      const dy = pos.y - clickY;
+      const d2 = dx * dx + dy * dy;
+      if (d2 < nearestDist2) {
+        nearestDist2 = d2;
+        nearestName = name;
+      }
+    });
+
+    if (nearestName) {
+      const sys = systems.get(nearestName)!;
+      // Place the menu at the system's on-screen position
+      const pt2 = svgRef.current.createSVGPoint();
+      pt2.x = positions[nearestName]!.x;
+      pt2.y = positions[nearestName]!.y;
+      const screenPoint = pt2.matrixTransform(svgRef.current.getScreenCTM()!);
+      setContextMenu({ x: screenPoint.x, y: screenPoint.y, system: sys });
+    }
+  };
+
   const handleContextMenu = (e: React.MouseEvent, system: System) => {
     e.preventDefault();
     e.stopPropagation();
@@ -623,6 +662,7 @@ export const RegionMap = ({ regionName, focusSystem, isCompact = false, isWormho
         onMouseLeave={handleMouseUp}
         onWheel={handleWheel}
         onDoubleClick={handleMapDoubleClick}
+        onContextMenu={handleBackgroundContextMenu}
       >
         <defs>
           <filter id="glow">