perf: fix chat timeouts during tool calls, reduce latency and UI jank

[karansinghgit]

Summary

• Fix watchdog timeout during tool execution — the 30s watchdog never reset while tools ran, causing "Model response timed out" on web search flows. Now resets on every delta and tool_status event. Increased to 60s for multi-round loops.
• Parallelize pre-flight operations — system prompt build + Brave key fetch now run concurrently via Promise.all. Removes duplicate getSettings() call.
• Stop writing settings.json on every read — getSettings() was doing a read+write cycle every call; now read-only.
• Cache context provider instances — TodoContextProvider and NotesContextProvider created once in constructor instead of re-allocated on every access.
• Reduce tool timeouts — fetch_url 15s→8s, web_search 10s→6s to reduce worst-case silence.
• Memoize remarkPlugins array — prevents React re-render waste.
• Debounce scroll-into-view — 80ms debounce prevents DOM thrashing during fast streaming.

Test plan

• Ask Robin to search the web (e.g., "what's the weather in London") — should NOT time out
• Verify streaming still scrolls smoothly
• Verify settings load correctly after storage read-only change
• Verify tool toggles still work in Settings

🤖 Generated with Claude Code