feat(dashboard): include historical sales in weekly chart

- loadWeeklyChart now fetches historical_sales for the last 7 days
- Sums normal daily sales + historical sales per day
- Bump dashboard.js to ?v=5

pos/templates/dashboard.html

@@ -568,7 +568,7 @@
   <script src="/pos/static/js/pos-utils.js?v=2" defer></script>
   <script src="/pos/static/js/sidebar.js" defer></script>
   <script src="/pos/static/js/dashboard-stats.js?v=3" defer></script>
-  <script src="/pos/static/js/dashboard.js?v=4" defer></script>
+  <script src="/pos/static/js/dashboard.js?v=5" defer></script>
   <script src="/pos/static/js/sync-engine.js" defer></script>
   <script>if('serviceWorker' in navigator){navigator.serviceWorker.register('/pos/sw.js',{scope:'/pos/'});}</script>
   <script src="/pos/static/js/pwa-install.js" defer></script>