Lite: Add Overview tab with resource chart grid (#689)

CONTEXT.md

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+# Session Context — 2026-03-26 08:15
+
+## Current Task
+Starting #689/#691 — Progressive server summary landing view with USE/RED/Golden Signals framing. These are being implemented together. Design sketch is on issue #691.
+
+## Decisions Made
+
+### Session-wide
+- Overlay on the slicer canvas, never on ScottPlot charts on other tabs (feedback saved)
+- Dots not lines for overlays — every execution gets a dot, no minimum threshold
+- Drill-down window ±30 min (±15 was too narrow, missed data due to spike chart zero-baseline rendering)
+- Custom date pickers must be populated on drill-down so user can explore other tabs
+- `_isRefreshing` guard needed on CustomDateRange_Changed/CustomTimeCombo_Changed/TimeRangeCombo_SelectionChanged to prevent cascading refreshes during programmatic picker updates
+- Chart drill-down added to all major charts, skipping Resource Metrics detail charts and Query Performance Trends pending #689/#691 consolidation
+- DuckDB path migrated to `%LOCALAPPDATA%\PerformanceMonitorLite\monitor.duckdb` — the old `bin/Debug` path has stale data
+
+### #689/#691 Design
+- Combined implementation: #691 provides framework vocabulary, #689 provides the UI
+- Replaces default landing tab (Wait Stats in Lite, Resource Overview in Dashboard)
+- All data sources already exist — aggregation + presentation only
+- Lite first, then Dashboard port
+- Investigate buttons reuse #684 pattern
+- USE Method sections: CPU, Memory, Disk I/O, TempDB, Workers (each with Utilization/Saturation/Errors)
+- RED Method section: Rate, Errors, Duration
+- Recent Incidents section: ranked problems with navigate links
+- Full design sketch posted on issue #691
+
+## Work Completed This Session
+
+### Issues closed:
+- #676 — CREATE DATABASE model DB size fix (PR #678)
+- #677 — Azure SQL DB server_id collision (community PR #680)
+- #681 — Slicer time range fixes + new slicers (PRs #697, #698)
+- #683 — Grid-to-slicer dot overlay (PRs #699, #700, #701)
+- #684 — Critical Issues investigate button (PR #702)
+- #682 — Chart drill-down (PRs #705, #706, #708, #709, #711, #714, #717)
+- #704 — Slicer custom range display fix (PR #707)
+- #694 — Support question answered
+- #695 — sp_BlitzLock debugging comment posted
+
+### Key PRs:
+- All merged to dev via squash+admin
+- Branch protection requires PRs — cannot push directly to dev
+
+## Work Remaining
+
+### Immediate: #689/#691
+- New `ServerSummaryControl` UserControl for Lite
+- Data aggregation queries pulling from existing DuckDB tables
+- USE/RED framework categorization
+- Severity thresholds per signal
+- Navigate-to-tab actions (pattern from #684)
+- Dashboard port after Lite validation
+
+### Deferred:
+- #686 — Unified query detail panel (too much work, needs #689 first)
+- #685 — Inline sparklines in grids
+- #687 — Before/after comparison for query grids
+- #688 — Correlated timeline lanes
+- #690 — Heatmap for query duration
+- #692 — Dynamic baselines (foundation for #693)
+- #693 — Anomaly detection
+- #696 — XE sessions stay running after Lite closes (design choice)
+- Dashboard port of remaining Resource Metrics drill-downs (post #689)
+- Dashboard chart time display mode for ScottPlot charts (pre-existing issue)
+
+## Important Context
+
+### File paths
+- Lite slicer: `Lite/Controls/TimeRangeSlicerControl.xaml.cs`
+- Dashboard slicer: `Dashboard/Controls/TimeRangeSlicerControl.xaml.cs`
+- Lite ServerTab: `Lite/Controls/ServerTab.xaml.cs` (~4500 lines)
+- Dashboard ServerTab: `Dashboard/ServerTab.xaml.cs` (~2000 lines)
+- Dashboard QueryPerformanceContent: `Dashboard/Controls/QueryPerformanceContent.xaml.cs`
+- DuckDB path: `C:/Users/edarl/AppData/Local/PerformanceMonitorLite/monitor.duckdb` (NOT the bin/Debug path)
+
+### Timezone notes
+- Server (sql2022): Pacific time (UTC-7 DST / UTC-8 standard)
+- User machine: Eastern time (UTC-4 DST / UTC-5 standard)
+- `ServerTimeHelper.UtcOffsetMinutes` is the SERVER's offset from UTC
+- Chart X-axis data is in server local time (UTC + UtcOffsetMinutes)
+- Hover helper returns server local time
+- Date pickers show user's local time
+- DuckDB stores collection_time in UTC
+
+### Git workflow
+- ALWAYS use feature branches + PRs (branch protection on dev and main)
+- `gh pr merge --squash --admin` to merge
+- Never push directly to dev — will be rejected
+
+### Build issues
+- `taskkill` not reliably killing processes this session — Defender or runtime holding file locks
+- User has to manually close apps before rebuild
+- Dashboard MCP server can also hold DLL locks

Lite/Controls/ServerTab.xaml

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         <TabControl Grid.Row="1" x:Name="MainTabControl" Background="{DynamicResource BackgroundBrush}"
                     BorderThickness="0" Padding="0" SelectionChanged="MainTabControl_SelectionChanged">
 
+            <!-- Overview Tab -->
+            <TabItem Header="Overview">
+                <Grid Margin="8">
+                    <Grid.RowDefinitions>
+                        <RowDefinition Height="*"/>
+                        <RowDefinition Height="*"/>
+                    </Grid.RowDefinitions>
+                    <Grid.ColumnDefinitions>
+                        <ColumnDefinition Width="*"/>
+                        <ColumnDefinition Width="*"/>
+                    </Grid.ColumnDefinitions>
+                    <Border Grid.Row="0" Grid.Column="0" Margin="0,0,4,4">
+                        <ScottPlot:WpfPlot x:Name="OverviewCpuChart"/>
+                    </Border>
+                    <Border Grid.Row="0" Grid.Column="1" Margin="4,0,0,4">
+                        <ScottPlot:WpfPlot x:Name="OverviewMemoryChart"/>
+                    </Border>
+                    <Border Grid.Row="1" Grid.Column="0" Margin="0,4,4,0">
+                        <ScottPlot:WpfPlot x:Name="OverviewFileIoChart"/>
+                    </Border>
+                    <Border Grid.Row="1" Grid.Column="1" Margin="4,4,0,0">
+                        <ScottPlot:WpfPlot x:Name="OverviewWaitStatsChart"/>
+                    </Border>
+                </Grid>
+            </TabItem>
+
             <!-- Wait Stats Tab -->
             <TabItem Header="Wait Stats">
                 <Grid Margin="8">