feat: add admin sales statistics dashboard with 5 analytics tabs

- Add sales stats API client with typed interfaces for all endpoints
- Implement AdminSalesStats page with summary cards and period selector
- Add TrialsTab with provider breakdown donut chart and daily area chart
- Add SalesTab with tariff/period breakdown and daily revenue chart
- Add RenewalsTab with period comparison and trend indicators
- Add AddonsTab with package breakdown bar chart
- Add DepositsTab with payment method breakdown bar chart
- Add SimpleBarChart, SimpleAreaChart, DonutChart components
- Add PeriodSelector with preset periods and custom date range
- Full responsive design (mobile/tablet/desktop/TG Mini App)
- ARIA accessibility (tablist, tab, tabpanel, aria-selected)
- Error handling with isError on all queries
- Empty data guards on all chart components
- i18n support across all 4 locales (en, ru, zh, fa)

src/components/sales-stats/TrialsTab.tsx

@@ -0,0 +1,86 @@
+import { useQuery } from '@tanstack/react-query';
+import { useTranslation } from 'react-i18next';
+
+import type { SalesStatsParams } from '../../api/adminSalesStats';
+import { salesStatsApi } from '../../api/adminSalesStats';
+import { SALES_STATS } from '../../constants/salesStats';
+import { StatCard } from '../stats';
+
+import { DonutChart } from './DonutChart';
+import { SimpleAreaChart } from './SimpleAreaChart';
+
+interface TrialsTabProps {
+  params: SalesStatsParams;
+}
+
+const PROVIDER_LABELS: Record<string, string> = {
+  telegram: 'Telegram',
+  email: 'Email',
+  vk: 'VK',
+  yandex: 'Yandex',
+  google: 'Google',
+  discord: 'Discord',
+};
+
+export function TrialsTab({ params }: TrialsTabProps) {
+  const { t } = useTranslation();
+
+  const { data, isLoading, isError } = useQuery({
+    queryKey: ['sales-stats', 'trials', params],
+    queryFn: () => salesStatsApi.getTrials(params),
+    staleTime: SALES_STATS.STALE_TIME,
+  });
+
+  if (isLoading) {
+    return (
+      <div className="animate-pulse space-y-4">
+        {Array.from({ length: 3 }, (_, i) => (
+          <div key={i} className="h-24 rounded-xl bg-dark-800/30" />
+        ))}
+      </div>
+    );
+  }
+
+  if (isError || !data) {
+    return <div className="py-8 text-center text-red-400">{t('admin.salesStats.loadError')}</div>;
+  }
+
+  const pieData = data.by_provider.map((item) => ({
+    name: PROVIDER_LABELS[item.provider] || item.provider,
+    value: item.count,
+    color: SALES_STATS.PROVIDER_COLORS[item.provider as keyof typeof SALES_STATS.PROVIDER_COLORS],
+  }));
+
+  const areaData = data.daily.map((item) => ({
+    date: item.date,
+    value: item.count,
+  }));
+
+  return (
+    <div className="space-y-4">
+      <div className="grid grid-cols-1 gap-3 sm:grid-cols-3">
+        <StatCard label={t('admin.salesStats.trials.total')} value={data.total_trials} />
+        <StatCard
+          label={t('admin.salesStats.trials.conversion')}
+          value={`${data.conversion_rate}%`}
+          valueClassName="text-success-400"
+        />
+        <StatCard
+          label={t('admin.salesStats.trials.avgDuration')}
+          value={`${data.avg_trial_duration_days} ${t('admin.trafficUsage.days')}`}
+        />
+      </div>
+
+      <div className="grid grid-cols-1 gap-4 lg:grid-cols-2">
+        <DonutChart data={pieData} title={t('admin.salesStats.trials.byProvider')} />
+        <SimpleAreaChart
+          data={areaData}
+          title={t('admin.salesStats.trials.dailyChart')}
+          chartId="trials-daily"
+          valueLabel={t('admin.salesStats.trials.registrations')}
+          color={SALES_STATS.PROVIDER_COLORS.telegram}
+        />
+      </div>
+    </div>
+  );
+}