⚡ Bolt: [performance improvement] Add React.memo for high-frequency WebSocket list rendering

[primoscope]

💡 What:

Added React.memo to DownloadItem (with a custom primitive property equality check) in ProgressPanel.tsx, and LogItem in LogPanel.tsx. Assigned a stable, unique ID to incoming logs instead of relying on array indices.

🎯 Why:

The ProgressPanel and LogPanel components render lists of items. Both lists are updated very frequently via WebSockets.
Because the parent components re-create the entire array objects immutably, all items in the list re-render on every single WebSocket message, even if only one download changed or only one log was appended. This causes significant CPU usage and jank, especially for many active downloads or long log outputs (which maxes at 1000). Array indices as keys on logs also forced complete re-renders when the array shifted.

📊 Impact:

Massively reduces re-renders of unchanged list items. For example, if there are 100 log items and 1 is added, the existing 100 will no longer re-render. If there are 10 active downloads and 1 progresses, the other 9 will not re-render. This drastically improves React rendering performance during high-frequency WebSocket updates and ensures UI stability.

🔬 Measurement:

Verified locally using Playwright integration tests mapping against a mock FastAPI backend. High-frequency simulated WebSocket payload ticks confirmed no regressions and functional state tracking. The TS compilation (pnpm run build) continues to pass successfully.

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PR created automatically by Jules for task 10593381347885775425 started by @dzp5103

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