closes#1803
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## Summary by cubic
Detects when the app was force-closed and shows a dialog with the last
known CPU and memory usage. Adds background performance monitoring so we
can surface metrics on next launch.
- **New Features**
- Start a performance monitor at app launch; captures process and system
memory/CPU every 30s and on quit.
- Persist metrics in settings.lastKnownPerformance and track
settings.isRunning to detect improper shutdowns.
- On startup, if the previous run was force-closed, send a
"force-close-detected" IPC event after the window loads.
- Add ForceCloseDialog to display timestamped process/system metrics.
- Whitelist the new IPC channel in preload and listen for it on the home
page.
<sup>Written for commit 0543cdc234da7f94024e8506749aaa9ca36ef916.
Summary will update automatically on new commits.</sup>
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