btdu.state: Fix sharing group linkage for duplicate browser paths

Split the sharing group linking loop into two passes to handle duplicate
browser paths correctly:
- First pass sets the next pointer for ALL pathData entries, including
  duplicates, because getNext uses findIndex which may return any
  matching index
- Second pass updates firstSharingGroup only for unique browser paths

This prevents incorrect linkage when the same browser path appears
multiple times in a sharing group's pathData, which can happen when
the same extent is used by the same file multiple times.

Author: CyberShadow

source/btdu/state.d

@@ -558,8 +558,17 @@ void populateBrowserPathsFromSharingGroup(
 			foreach (i, ref path; paths)
 			{
 				auto browserPath = group.pathData[i].path;
+				// Set next pointer to the current head of the list.
+				// This must be done for ALL pathData entries, even duplicates,
+				// because getNext uses findIndex which may return any matching index.
 				group.pathData[i].next = browserPath.firstSharingGroup;
-				browserPath.firstSharingGroup = group;
+			}
+			// Now update firstSharingGroup for each unique browserPath
+			foreach (i, ref path; paths)
+			{
+				auto browserPath = group.pathData[i].path;
+				if (browserPath.firstSharingGroup != group)
+					browserPath.firstSharingGroup = group;
 			}
 		}
 		else