feat: add recharts analytics to admin campaign stats page

- Move shared chart components (DailyChart, PeriodComparison, StatCard) to src/components/stats/ with configurable label props
- Create shared types for chart data decoupled from partner API
- Add campaign chart data API client with deposits/spending split
- Enhance AdminCampaignStats with daily trends chart, period comparison, top registrations, and deposit/spending stat cards
- Add useChartColors hook with SSR guard and theme-aware CSS variable parsing
- Add cross-platform clipboard utility with execCommand fallback for Telegram WebView
- Add i18n keys for chart analytics across all 4 locales (en, ru, zh, fa)
- Responsive fixes: truncation for long names/values, responsive text sizing, touch-friendly copy buttons

src/components/stats/StatCard.tsx

@@ -0,0 +1,27 @@
+import { type ReactNode } from 'react';
+
+const DEFAULT_VALUE_CLASS = 'text-dark-100';
+
+interface StatCardProps {
+  label: string;
+  value: string | number;
+  icon?: ReactNode;
+  valueClassName?: string;
+}
+
+export function StatCard({
+  label,
+  value,
+  icon,
+  valueClassName = DEFAULT_VALUE_CLASS,
+}: StatCardProps) {
+  return (
+    <div className="rounded-xl bg-dark-800/30 p-3">
+      <div className="flex items-center gap-1.5 text-sm text-dark-500">
+        {icon}
+        <span>{label}</span>
+      </div>
+      <div className={`mt-1 text-base font-semibold sm:text-lg ${valueClassName}`}>{value}</div>
+    </div>
+  );
+}