Audit and simplify demo dashboard layout code

[michaelw]

Summary

The demo dashboard layout and UI code has accumulated several small iterative fixes while tuning the Keycloak scenario workflow. The current behavior is acceptable, but the CSS/layout structure should be audited and simplified if possible without making meaningful UX compromises.

Goals

• Review the dashboard layout structure and CSS after the recent tab, scenario list, token, response, and policy panel changes.
• Simplify the layout code where it can be made easier to reason about.
• Reduce fragile height, overflow, and nested-scroll interactions.
• Preserve the current useful behavior: stable scenario list, equal-height tab panes, readable token/policy/response/log views, and responsive usability.

Acceptance Criteria

• Layout code is easier to understand and has fewer special-case height/overflow rules where practical.
• Dashboard tabs remain visually consistent and do not introduce large unused gaps or unnecessary nested scrollbars.
• Token, response, policy, logs, and diagram views remain usable at common desktop viewport sizes.
• Existing dashboard tests and static checks pass.

Notes

This is intentionally low priority. It should not block the Keycloak e2e/demo work unless a concrete layout bug resurfaces.