⚡ Bolt: Replace O(N) array reduction with O(1) turn sum in DeckShowcase

[google-labs-jules]

💡 What: Modified useWinData to pre-calculate the running sum of win turns and passed it to DeckShowcase.
🎯 Why: Replaced an O(N) array reduction inside a useMemo block which could become slow when processing simulations with thousands of games.
📊 Impact: Turns O(N) array reductions into O(1) computations in DeckShowcase list rendering.
🔬 Measurement: Verified by running all existing tests via scripts/test.sh.

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PR created automatically by Jules for task 4795030533218234065 started by @TytaniumDev

[google-labs-jules]

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