Improve doc generation with scrollable text-only output

[mdmaas]

• Long output is rendered as a pre inside .jp-RenderedText.jp-OutputArea-output in the generated page, and the new selector targets exactly that structure.
• The max-height and overflow-y are enforced with !important on that pre, so plugin/theme defaults should not override it.
• HTML/interactive outputs are explicitly excluded from clipping by setting max-height none and overflow visible.