Keep Battle Tanks result actions reachable in short arenas

[bashmohandes]

Motivation

• On narrow non-fullscreen phones the 16:9 arena can be very short and the result card's actions were being clipped and unreachable because the card used overflow:hidden and the arena parent has overflow:hidden; the result UI must remain reachable (Rematch/Share) on small viewports.

Description

• Constrain the result card to the available arena height and allow internal vertical scrolling by updating .result-card in battle-tanks/styles.css to include box-sizing:border-box, max-height:100%, overflow-y:auto, and overscroll-behavior:contain and remove the clipping overflow:hidden behavior.
• Add a regression test in tests/battle-tanks-page.test.js that asserts the presence of the scrollable result-card contract and ensures overflow:hidden is not present on .result-card.

Testing

• Ran the full test suite with npm test and all automated tests passed (168 passed, 0 failed).
• Ran the focused test pattern for the new check with npm test -- --test-name-pattern='Battle Tanks keeps result actions reachable|Battle Tanks game-over actions' and both tests passed.
• Ran the automated style/type checks with npm run check and git diff --check, both completed without errors.

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Codex Task