Summary

• Migrates 5 DataGrids from the old TextBox-in-header filter style to the standard popup filter pattern
• DefaultTraceContent: DefaultTraceEventsDataGrid (7 cols), TraceAnalysisDataGrid (9 cols)
• CurrentConfigContent: ServerConfigDataGrid (9 cols), DatabaseConfigDataGrid (5 cols), TraceFlagsDataGrid (5 cols — previously had no filters at all)
• All 35 columns now have consistent popup filter buttons with operator support and gold active-filter indicators

Fixes #200.

Test plan

• Build succeeds with zero warnings
• Default Trace Events: popup filters on all 7 columns, filter/clear works, gold icon when active
• Trace Analysis: popup filters on all 9 columns
• Server Configuration: popup filters on all 9 columns (6 previously unfiltered)
• Database Configuration: popup filters on all 5 columns (1 previously unfiltered)
• Trace Flags: popup filters on all 5 columns (previously had none)
• Multi-grid routing: filtering on one grid doesn't interfere with another

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