Lite: Add column-level filtering to data grids

[erikdarlingdata]

Description

The Dashboard has column-level filtering on all data grids (via ColumnFilterPopup, DataGridFilterService, ColumnFilterState, FilterOperator), but Lite has no equivalent functionality. Users should be able to filter grid data by column values in Lite the same way they can in the Dashboard.

Dashboard components to port

• ColumnFilterPopup.xaml / .xaml.cs — filter UI popup
• DataGridFilterService.cs — applies filters to DataGrid views
• ColumnFilterState.cs — tracks filter state per column
• FilterOperator.cs — filter operator model (contains, equals, etc.)

Affected grids

All data grid tabs in Lite (query snapshots, blocking, wait stats, etc.)

[erikdarlingdata]

Implemented in PR #26. All 11 Lite DataGrids now have column-level filtering with operator selection, filter persistence across refreshes, and visual feedback (gold/dim icons).