feat: enhance sales stats with device stats, per-tariff charts, and dual-series trials

- Add DualAreaChart component for two-series visualization (registrations vs trials)
- Add MultiSeriesAreaChart component for N-series tariff breakdown with dynamic pivoting
- AddonsTab: add device purchases and device revenue stat cards
- SalesTab: add per-tariff daily sales chart using MultiSeriesAreaChart
- TrialsTab: replace single-series area chart with dual-series registrations + trials chart
- Update TypeScript interfaces to match backend schema changes
- Add i18n keys for all new UI elements across en, ru, zh, fa locales

src/components/sales-stats/DualAreaChart.tsx

@@ -0,0 +1,151 @@
+import { useMemo } from 'react';
+import { useTranslation } from 'react-i18next';
+import {
+  Area,
+  AreaChart,
+  CartesianGrid,
+  Legend,
+  ResponsiveContainer,
+  Tooltip,
+  XAxis,
+  YAxis,
+} from 'recharts';
+
+import { SALES_STATS } from '../../constants/salesStats';
+import { useChartColors } from '../../hooks/useChartColors';
+
+interface DualAreaChartProps {
+  data: { date: string; series1: number; series2: number }[];
+  title: string;
+  chartId: string;
+  series1Label: string;
+  series2Label: string;
+  series1Color?: string;
+  series2Color?: string;
+  height?: number;
+}
+
+export function DualAreaChart({
+  data,
+  title,
+  chartId,
+  series1Label,
+  series2Label,
+  series1Color,
+  series2Color,
+  height = SALES_STATS.CHART.HEIGHT,
+}: DualAreaChartProps) {
+  const { t, i18n } = useTranslation();
+  const colors = useChartColors();
+  const color1 = series1Color || colors.referrals;
+  const color2 = series2Color || colors.earnings;
+
+  const chartData = useMemo(
+    () =>
+      data.map((item) => ({
+        ...item,
+        label: new Date(item.date + 'T00:00:00').toLocaleDateString(i18n.language, {
+          month: 'short',
+          day: 'numeric',
+        }),
+      })),
+    [data, i18n.language],
+  );
+
+  if (data.length === 0) {
+    return (
+      <div className="bento-card">
+        <h4 className="mb-3 text-sm font-semibold text-dark-200">{title}</h4>
+        <div className="flex items-center justify-center text-sm text-dark-400" style={{ height }}>
+          {t('common.noData')}
+        </div>
+      </div>
+    );
+  }
+
+  return (
+    <div className="bento-card">
+      <h4 className="mb-3 text-sm font-semibold text-dark-200">{title}</h4>
+      <ResponsiveContainer width="100%" height={height}>
+        <AreaChart data={chartData} margin={SALES_STATS.CHART.MARGIN}>
+          <defs>
+            <linearGradient id={`gradient-s1-${chartId}`} x1="0" y1="0" x2="0" y2="1">
+              <stop
+                offset={SALES_STATS.GRADIENT.START_OFFSET}
+                stopColor={color1}
+                stopOpacity={SALES_STATS.GRADIENT.START_OPACITY}
+              />
+              <stop
+                offset={SALES_STATS.GRADIENT.END_OFFSET}
+                stopColor={color1}
+                stopOpacity={SALES_STATS.GRADIENT.END_OPACITY}
+              />
+            </linearGradient>
+            <linearGradient id={`gradient-s2-${chartId}`} x1="0" y1="0" x2="0" y2="1">
+              <stop
+                offset={SALES_STATS.GRADIENT.START_OFFSET}
+                stopColor={color2}
+                stopOpacity={SALES_STATS.GRADIENT.START_OPACITY}
+              />
+              <stop
+                offset={SALES_STATS.GRADIENT.END_OFFSET}
+                stopColor={color2}
+                stopOpacity={SALES_STATS.GRADIENT.END_OPACITY}
+              />
+            </linearGradient>
+          </defs>
+          <CartesianGrid strokeDasharray={SALES_STATS.GRID_DASH} stroke={colors.grid} />
+          <XAxis
+            dataKey="label"
+            tick={{ fill: colors.tick, fontSize: SALES_STATS.AXIS.TICK_FONT_SIZE }}
+            tickLine={false}
+            interval="preserveStartEnd"
+          />
+          <YAxis
+            tick={{ fill: colors.tick, fontSize: SALES_STATS.AXIS.TICK_FONT_SIZE }}
+            tickLine={false}
+            axisLine={false}
+            width={SALES_STATS.AXIS.WIDTH}
+            allowDecimals={false}
+          />
+          <Tooltip
+            contentStyle={{
+              backgroundColor: colors.tooltipBg,
+              border: `1px solid ${colors.tooltipBorder}`,
+              borderRadius: SALES_STATS.TOOLTIP.BORDER_RADIUS,
+              fontSize: SALES_STATS.TOOLTIP.FONT_SIZE,
+            }}
+            labelStyle={{ color: colors.label }}
+            formatter={(value: number | undefined, name: string | undefined) => {
+              const displayValue = value ?? 0;
+              if (name === 'series1') return [displayValue, series1Label];
+              return [displayValue, series2Label];
+            }}
+          />
+          <Legend
+            formatter={(value: string) => {
+              if (value === 'series1') return series1Label;
+              return series2Label;
+            }}
+          />
+          <Area
+            type="monotone"
+            dataKey="series1"
+            name="series1"
+            stroke={color1}
+            fill={`url(#gradient-s1-${chartId})`}
+            strokeWidth={SALES_STATS.STROKE_WIDTH}
+          />
+          <Area
+            type="monotone"
+            dataKey="series2"
+            name="series2"
+            stroke={color2}
+            fill={`url(#gradient-s2-${chartId})`}
+            strokeWidth={SALES_STATS.STROKE_WIDTH}
+          />
+        </AreaChart>
+      </ResponsiveContainer>
+    </div>
+  );
+}