The legacy chart was a stacked BarChart, not a LineChart — the initial 'line'
naming was misleading. Rename internal type, i18n key (chartLine -> chartBar,
Lignes -> Barres, Lines -> Bars) and icon. Legacy 'line' in localStorage is
migrated to 'bar' on read.
Adds a segmented chart-type toggle to the /reports/trends "By category"
sub-view that switches between the existing stacked bars (default,
unchanged) and a new Recharts AreaChart with stackId="1" showing total
composition over time. Both modes share the same category palette and
SVG grayscale patterns so the visual signature is preserved.
- CategoryOverTimeChart gains a chartType: 'line' | 'area' prop
(default 'line' for backward compatibility with the dashboard usage).
- New TrendsChartTypeToggle component, persisted in localStorage under
"reports-trends-category-charttype".
- Toggle only renders in the "By category" sub-view with chart view
mode selected; hidden otherwise.
- i18n keys reports.trends.chartLine / chartArea / chartTypeAria in
FR and EN.
- CHANGELOG entries in both languages.