refactor: centralize multi-card bring-to-front logic and document new spatial workspace architecture.

frontend/src/desktop/LayoutSystem.ts

@@ -274,7 +274,6 @@ export class LayoutStore {
             const dx = card.x - x;
             const dy = card.y - y;
 
-            // Check if center is within inner radius of top card
             // Use squared distance to avoid sqrt
             const distSq = dx * dx + dy * dy;
             if (distSq < radius * radius) {
@@ -296,6 +295,20 @@ export class LayoutStore {
             .map(c => c.id);
     }
 
+    bringToFront(ids: string[]) {
+        const cards = ids
+            .map(id => this.items.get(id))
+            .filter((c): c is LayoutCard => !!c);
+
+        // Sort by current Z-index to preserve relative order
+        cards.sort((a, b) => a.z - b.z);
+
+        // Assign new Z-indices
+        for (const card of cards) {
+            card.update({ z: this.zCounter++ });
+        }
+    }
+
     getSnapshot() {
         return Array.from(this.items.values()).map(card => card.toSnapshot());
     }