Fix missing Gravity slider in production by allowing panel scroll

[Testtesttestestes]

Motivation

• The bottom control panel was being clipped in production builds on short viewports, which hid lower controls such as the Gravity slider.

Description

• Constrained the control panel height and enabled vertical scrolling by updating src/App.tsx.
• Added the Tailwind classes max-h-[calc(100vh-3rem)] and overflow-y-auto to the panel wrapper so lower controls remain reachable.

Testing

• Ran npm run build and it completed successfully.
• Ran npm run lint (tsc --noEmit) and it passed with no errors.
• Launched a preview and captured an automated screenshot of the updated UI to validate the panel is scrollable and the Gravity slider is visible.

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Codex Task