fix: improve campaign stats, shared chart components, and i18n coverage

- Extract shared chart constants to constants/charts.ts
- Add TREND_STYLES to stats/constants.ts for reuse
- Fix useChartColors with MutationObserver for theme changes
- Fix DailyChart date parsing to prevent timezone shift
- Add truncate to StatCard value for overflow safety
- Fix CampaignCard copy feedback inside try block
- Add NaN validation and staleTime to AdminCampaignStats
- Replace hardcoded strings with i18n keys in Referral page
- Add missing i18n keys across all 4 locales (en, ru, zh, fa)
- Add sales stats route to AdminPanel and App router

src/components/stats/DailyChart.tsx

@@ -42,7 +42,7 @@ export function DailyChart({ data, chartId, title, earningsLabel, countLabel }:
       data.map((item) => ({
         ...item,
         earnings_display: item.earnings_kopeks / PARTNER_STATS.KOPEKS_DIVISOR,
-        label: new Date(item.date).toLocaleDateString(i18n.language, {
+        label: new Date(item.date + 'T00:00:00').toLocaleDateString(i18n.language, {
           month: 'short',
           day: 'numeric',
         }),