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/locales/en.json

@@ -3776,6 +3776,10 @@
       "discountOverridesHint": "Leave empty to use global discount",
       "discountPreview": "Preview",
       "discountActive": "Discount",
+      "background": "Animated background",
+      "analytics": "Analytics",
+      "viewGoal": "View goal",
+      "clickGoal": "Payment click goal",
       "statistics": "Statistics",
       "stats": {
         "title": "Landing Statistics",
@@ -3796,7 +3800,8 @@
         "successful": "Successful",
         "funnel": "Funnel",
         "loadError": "Failed to load statistics",
-        "noPurchases": "No purchases"
+        "noPurchases": "No purchases",
+        "paid": "paid"
       },
       "purchases": {
         "title": "Purchases",