Remove query history sync from iCloud Sync

[datlechin]

Summary

• Removed query history sync from iCloud Sync — history stays local-only
• Removed syncQueryHistory, historySyncLimit, and HistorySyncLimit enum from SyncSettings
• Cleaned up push/pull/conflict handling in SyncCoordinator and SyncRecordMapper
• Removed sync-tracking columns (is_synced) and methods from QueryHistoryStorage
• Updated settings UI and docs

Test plan

• Build succeeds with no compilation errors
• Existing iCloud Sync still works for connections, groups, settings, SSH profiles
• Sync Settings view no longer shows "Query History" toggle or "History Limit" picker
• Query history still records and displays locally