Bonsai: custom display names for links

Each link row draws an editable display_name (double-click to rename)
with the file path as placeholder while unset, so several links of the
same file can be told apart. The name persists in the same Description
JSON blob as the filter and loaded state (new name key, written at
save time and by reload_link), restores on project open, and plain
legacy strings still decode unchanged. Decode tests updated to the
four-tuple with a name round-trip case.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/dev-notes/linked-file-features.md

@@ -122,9 +122,12 @@ default set when empty) − exclude, applied in `LoadLinkedProject` and per link
   alone would let same-include/different-exclude links silently serve each other's
   geometry.
 - **Persistence**: `encode_link_filter`/`decode_link_filter` — a plain include is
-  stored in `Description` as-is (backwards compatible); an exclude promotes the
-  value to `{"include": …, "exclude": …}` JSON. Decode treats non-JSON as a legacy
-  include string.
+  stored in `Description` as-is (backwards compatible); an exclude, a `loaded`
+  state or a custom display name promotes the value to
+  `{"include": …, "exclude": …, "loaded": …, "name": …}` JSON. Decode treats
+  non-JSON as a legacy include string. The display name (`Link.display_name`,
+  double-click the list row to rename; file path shows as placeholder while
+  unset) exists to tell apart several links of the same file.
 - Exclude applies on top of the **default** element set too, so
   "everything except X" needs no explicit include.
 - UI labels are **Include**/**Exclude** (matching the drawing pattern), but the