feat: landing analytics goals, daily bar chart, referrer tracking, contact persistence

- Add per-landing analytics goals (view/click) with admin editor toggle
- Add sticky pay button option for mobile landing pages
- Add daily purchases bar chart (created vs paid) to landing stats
- Replace single purchase count with created/paid split in stats summary
- Add referrer tracking to purchases with hostname display in stats
- Add time display to purchase cards alongside date
- Pass user timezone to stats API for correct daily grouping
- Clamp referrer (500 chars) and subid (255 chars) to backend limits
- Persist contact value per-landing-slug in localStorage
- Fire buy_success analytics goal on successful delivery
- Export USER_TIMEZONE from format utils
- Add analytics/stats translations for fa.json and zh.json locales

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/utils/format.ts

@@ -1,3 +1,5 @@
+export const USER_TIMEZONE = Intl.DateTimeFormat().resolvedOptions().timeZone || 'UTC';
+
 export function formatUptime(seconds: number): string {
   const days = Math.floor(seconds / 86400);
   const hours = Math.floor((seconds % 86400) / 3600);