fix(ui): remove ScrollArea for fully adaptive window height

Remove ScrollArea wrapper — content is laid out directly in CentralPanel
at its natural height. Window resizes to fit via ViewportCommand::InnerSize,
matching the Python launcher's no-scroll behavior. Capped at 800px max.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: RMANOV