perf(messages): reduce rerenders during streaming

[VikashLoomba]

Summary

• Move timer rendering into a memoized WorkingIndicator and memoize per-item rows so only the active/changed item re-renders.
• Remove the per-second full-list re-render during streaming while preserving existing UI behavior.

Perf Validation

Methodology:

• Local jsdom harness with 200 message items.
• Mocked Markdown component to count renders.
• Compared current implementation vs a legacy model (timer state in parent + no memoized rows).

Results:

• Timer tick (1s while thinking): current 0 Markdown renders vs legacy 200 (200× fewer).
• Streaming delta (update last item): current 1 render vs legacy 200 (~200× fewer).

Note: harness was temporary and not committed; results recorded during local run.

Testing

• npm run lint
• npm run test
• npm run typecheck

[Copilot]

Pull request overview

This PR optimizes rendering performance during message streaming by isolating timer updates and memoizing individual message rows. The key optimization moves timer state management into a memoized WorkingIndicator component, preventing unnecessary rerenders of message items when only the timer updates.

Changes:

• Extracted message rendering logic into memoized row components (MessageRow, ReasoningRow, ReviewRow, DiffRow, ToolRow)
• Created a memoized WorkingIndicator component with isolated timer state
• Wrapped callback functions with useCallback for stable references across renders

Reviewed changes

Copilot reviewed 1 out of 2 changed files in this pull request and generated no comments.

File	Description
src/features/messages/components/Messages.tsx	Refactored Messages component to use memoized row components and moved timer state to WorkingIndicator, achieving ~200× reduction in rerenders during streaming
package-lock.json	Updated dependency metadata by removing "peer": true flags from various packages

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Dimillian]

This is really good, thanks!