Add a configurable range option (7/30/60/90/180/365 days) for heartbeat bars on status pages.
This allows status page owners to customize how much historical data is shown to visitors.
Changes:
- Add database migration for heartbeat_bar_range_days column
- Update StatusPage model to include heartbeat bar range setting
- Modify heartbeat API endpoint to respect configured range
- Add UI controls in status page editor for range selection
- Update English translations for new settings
- Default to 90 days for backward compatibility
Resolves#1888
