Update default theme to light and fix data source subtitle

Default to light theme instead of system preference, and update
dashboard subtitle to reflect VivaTicket as the data source.

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

src/locales/ar.json

@@ -56,7 +56,7 @@
   },
   "dashboard": {
     "title": "لوحة التحكم",
-    "subtitle": "تحليلات المتاحف المباشرة من جداول بيانات Google",
+    "subtitle": "تحليلات المتاحف من تقارير مبيعات VivaTicket",
     "noData": "لا توجد بيانات",
     "noDataMessage": "لا توجد سجلات تطابق الفلاتر الحالية. حاول تعديل اختيارك.",
     "quarterlyComparison": "مقارنة ربع سنوية: 2024 مقابل 2025",

src/locales/en.json

@@ -56,7 +56,7 @@
   },
   "dashboard": {
     "title": "Dashboard",
-    "subtitle": "Real-time museum analytics from Google Sheets",
+    "subtitle": "Museum analytics from VivaTicket Sales Reports",
     "noData": "No data found",
     "noDataMessage": "No records match your current filters. Try adjusting your selection.",
     "quarterlyComparison": "Quarterly Comparison: 2024 vs 2025",