fix(css): add sidebar offset (260px) to all main content areas

The sidebar injected by sidebar.js is position:fixed with width:260px,
but most pages lacked margin-left on their main content, causing text
to be hidden behind the sidebar.

Affected pages:
- accounting, config, inventory, invoicing (.main)
- catalog, customers, diagrams, reports (.main-content)

Already fixed: dashboard, quotations
Not affected: fleet, whatsapp (use pos-main-offset), pos (no sidebar)

pos/static/css/diagrams.css

@@ -76,6 +76,7 @@
     .main-content {
       flex: 1; display: flex; flex-direction: column; overflow: hidden;
       min-width: 0;
+      margin-left: 260px;
     }
 
     .page-header {