Show only constructor names in data fam-instance node labels

Show only constructor names in data fam-instance node labels

Node labels for data fam-instances now read `Family args = ConA |
ConB` instead of `Family args = ConA Int Bool | ConB { x :: Char }`.
Fields just pad the node visually and are rarely interesting at a
glance. The side panel still renders the full constructor
declaration (name + arg types or record fields) for when the detail
is wanted.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>