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/catalog.css

@@ -76,7 +76,7 @@
        MAIN CONTENT
        ========================================================================= */
 
-    .main-content { flex: 1; display: flex; flex-direction: column; overflow: hidden; min-width: 0; }
+    .main-content { flex: 1; display: flex; flex-direction: column; overflow: hidden; min-width: 0; margin-left: 260px; }
 
     /* Header with breadcrumb + search */
     .content-header {