Renders a Chart.js grouped bar chart with one or two data series using theme colours.
BAR — set as ReportType in def_report.
def Render(self, Param1="", Param2="", Param3="") -> str:
Parameters are unused. Expects the query to return rows with: [0] X-axis label, [1] primary series value, and optionally [2] secondary series value. Series labels are taken from FieldNames. Returns an HTML string containing a <canvas> element and Chart.js initialisation script.
Requires chart.min.js (added via self.Parent.add_resource_script). Uses $theme-primary$ and $theme-secondary$ palette placeholders for bar colours. Both Y and X axis gridlines are enabled; axes are not stacked.