`class Dog < Animal` exposes the base in the `superclass` field, but the
inheritance handler in `_extract_generic` had branches for
java/kotlin/c#/scala/cpp/php/swift/python and none for Ruby, so every Ruby
`inherits` edge was silently dropped (contains/methods/calls unaffected).
Add a Ruby branch that reads the `superclass` field, handling both a bare
`constant` (`< Animal`) and a `scope_resolution` (`< Foo::Bar` -> Bar).
Adds a subclass to the Ruby fixture and a regression test.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>