⚡ Bolt: [performance improvement] Optimize handleAgentEvents batch processing

[iotserver24]

💡 What: Refactored the handleAgentEvents batch processing loop in packages/desktop/src/renderer/App.tsx. Replaced inner O(N) backward-searching functions (findLastAssistantStreaming and findLastToolCall) with pre-calculated indices (lastAssistantIndex and pendingToolIndices). These cached values are explicitly updated inside the inner batch loop to maintain synchronization.
🎯 Why: The prior implementation performed an O(N) array search inside an O(M) loop whenever resolving a batch of streaming events. In a long session context, this produces severe O(NM) complexity, forcing the UI thread to freeze and stutter when rendering large bursts of tool call or text streaming data.
📊 Impact: Reduces time complexity of agent event resolution from O(NM) to O(N+M), lowering garbage collection spikes and making the UI substantially more responsive when rendering hundreds of streamed events over thousands of message history elements.
🔬 Measurement: Test streaming performance by launching a query that produces heavy text streaming or rapid sequential tool calls against a deeply populated conversation history. Observe the elimination of noticeable UI thread blocking during the operation. Verified via pnpm test and pnpm lint. Visual layout verified using Playwright. Critical learnings on O(N*M) list resolution logged to .jules/bolt.md.

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PR created automatically by Jules for task 4847439611447378306 started by @iotserver24

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