fix: FileTree backend recursion breaking lazy loading

CRITICAL FIX: Remove recursion from listDirectoryForTree function.

The backend was recursively fetching ALL subdirectories and returning
them as a flat list, which completely broke the lazy-loading model.

Changes:
- Remove recursive call in listDirectoryForTree
- Backend now returns ONLY immediate children
- Frontend handles lazy loading by requesting children on expand
- This matches the intended architecture where frontend controls tree

This fixes the issue where directory contents were duplicated and
the tree structure was corrupted when expanding/collapsing.

gadget-drone/src/gadget-drone.ts

@@ -835,17 +835,8 @@ class GadgetDrone extends GadgetProcess {
 
       results.push(fileTreeEntry);
 
-      // Recurse if directory and within depth limit
-      if (entry.isDirectory() && depth < maxDepth) {
-        const subResults = await this.listDirectoryForTree(
-          fullPath,
-          showHidden,
-          depth + 1,
-          maxDepth,
-          projectRoot,
-        );
-        results.push(...subResults);
-      }
+      // NO RECURSION - lazy loading is handled by frontend
+      // The frontend will request children when directories are expanded
     }
 
     return results;