Render multi-arg superclass edge labels as {a} {b}, not (a, b)

Render multi-arg superclass edge labels as {a} {b}, not (a, b)

The tuple-shaped label `(a, b)` looked like the Haskell tuple type
`(a, b)`, but it's actually a positional list of args being passed
to the superclass — not packed into a pair. Switch to space-
separated brace-wrapped form `{a} {b}` so the positional shape
reads at a glance. Single-arg labels stay bare since there's no
ambiguity.

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