Family node labels show tyvars, with (data) on its own italic line

Family node labels show tyvars, with (data) on its own italic line

Family nodes now carry their tyvars in the label (e.g. @BftDSIGN c@,
@LedgerState blk mk@), matching the recent class-node tyvar change.
For data families, @(data)@ goes on a new line via @\n@ in the
label and the cytoscape stylesheet italicises the whole node label
via @node[kind = "family"][?isData]@.

Cytoscape can't style only one line of a label, so the family name
itself ends up italicised too. That's a deliberate trade-off — the
italic doubles as a "this is a data family, not a type family" cue
without requiring any additional iconography.

Render.hs's familyNodeLabel and viewer.js's ensureFamilyNode +
focused-family-node code path all updated together so the
classes-view, instance-view and family-view family nodes all read
the same way.

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