feat: implement SelectionEngine with rbush hit testing

frontend/src/interaction/SelectionEngine.ts

@@ -0,0 +1,47 @@
+import RBush from 'rbush';
+
+class SelectionEngine {
+  private rbush: RBush<any>;
+
+  constructor() {
+    this.rbush = new RBush();
+  }
+
+  // Single click selection
+  selectSingle(x: number, y: number): any[] {
+    // Implementation for single click selection
+    return [];
+  }
+
+  // Window selection (left-to-right)
+  selectWindow(startX: number, startY: number, endX: number, endY: number): any[] {
+    // Implementation for window selection
+    return [];
+  }
+
+  // Crossing selection (right-to-left)
+  selectCrossing(startX: number, startY: number, endX: number, endY: number): any[] {
+    // Implementation for crossing selection
+    return [];
+  }
+
+  // Fence selection (polyline crossing)
+  selectFence(points: {x: number, y: number}[]): any[] {
+    // Implementation for fence selection
+    return [];
+  }
+
+  // Quick-select (by layer/type/color)
+  quickSelect(criteria: {layer?: string, type?: string, color?: string}): any[] {
+    // Implementation for quick-select
+    return [];
+  }
+
+  // Lasso selection
+  selectLasso(points: {x: number, y: number}[]): any[] {
+    // Implementation for lasso selection
+    return [];
+  }
+}
+
+export default SelectionEngine;