Add ref path and dedup integration plan

- Introduced a new plan file detailing the integration of ref path handling and deduplication cleanup processes.
- Implemented a `tentative_fs_path()` function to build filesystem-compatible paths, addressing issues with slugified and deduplicated instance names.
- Enhanced the `handle_tree_event()` method in the change processor to trigger dedup cleanup actions upon deletions, ensuring proper management of dedup groups.
- Updated relevant files to replace legacy path handling with the new system, improving overall path resolution and cleanup efficiency.

These changes enhance the robustness of path handling and deduplication processes, paving the way for improved project management and user experience.

src/web/api.rs

@@ -2640,7 +2640,7 @@ impl ApiService {
                         remove_attributes.push(attr_name);
                     } else if tree.get_instance(*target_ref).is_some() {
                         // Valid target: compute path and add as Rojo_Ref_* attribute
-                        let path = crate::ref_target_path_from_tree(&tree, *target_ref);
+                        let path = crate::ref_target_path_from_tree(tree, *target_ref);
 
                         // Warn if the path is ambiguous (duplicate-named siblings
                         // at any ancestor level). The ref will still be written,