[Insights][R4][App] Support count metrics in charts and data tables #102808

Implement this section of the design doc: Support the count metric in charts.

Description

Allow Compliance charts and their data tables to display counts while preserving the existing amount behavior for Search, Home, and Spend.

• Introduce SearchChartMetric = amount | count, add metric to InsightsChartSpec, and pass it from InsightsChartWidget to SearchChartView, defaulting to amount.
• Update buildFlatSeries to read the grouped row's count for count metrics. Amount metrics continue reading total and converting from the currency's minor units.
• Apply the selected metric to current and comparison series, including Average baselines and deltas.
• Resolve the metric's value formatter in SearchChartView and pass it through SearchChartProps to BarChart, LineChart, and PieChart.
• Update useChartLabelFormats so axes, plotted-value labels, pie totals, and tooltips use the selected formatter. Counts use numberFormat without a currency unit.
• Pass the metric and formatter through renderDetails so InsightsDataTable displays the same values as the chart.

Acceptance criteria

• Counts display without currency units or currency minor-unit conversion.
• Current values, comparisons, Average baselines, and deltas use the selected metric consistently.
• Chart labels, tooltips, totals, and data tables agree.
• Existing Search, Home, and Spend charts retain their amount behavior.
• Include relevant series-construction tests and manual chart/table regression steps.