⚡ Bolt: [performance improvement] Optimize ProductCard and CartContext

[Dev22603]

💡 What:

1. Wrapped ProductCard component in React.memo().
2. Removed two unused, block-scoped calculations (totalPrice, totalQuantity) in CartContext.jsx that were firing on every cartItems change.

🎯 Why:

1. ProductCard was unnecessarily re-rendering on every keystroke when users typed in the search bar on Home.jsx because the parent Home component updated its local state.
2. The useEffects in CartContext.jsx were consuming CPU cycles iterating over cartItems without saving or using the computed results.

📊 Impact:

• Significantly reduces re-renders of ProductCard components during search input.
• Saves CPU cycles by removing O(N) redundant calculations on every cart change.

🔬 Measurement:

• Verify with React DevTools Profiler that ProductCard no longer re-renders when updating the search input in Home.jsx.
• Build, linting passes and application runs successfully.

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PR created automatically by Jules for task 15870412287671141728 started by @Dev22603

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