feat: UX improvements — nav, reports tabs, dashboard alerts, transaction hints, settings layout

- Move Reports to Finans nav group and auto-expand Övrigt on its pages
- Make report tabs horizontally scrollable with gradient fade on mobile
- Surface deadlines and alerts above the fold on dashboard
- Add dismissible categorization hint card on transactions page
- Split settings company form into 4 separate Cards for scannability
- Add monthly breakdown report, document upload zone, journal entry attachments
- Add batch category selector, receipt document linking, invoice form improvements

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/globals.css

@@ -278,6 +278,15 @@ h1, h2, h3 {
   background: hsl(var(--muted-foreground) / 0.3);
 }
 
+/* Hide scrollbar utility */
+.scrollbar-hide {
+  -ms-overflow-style: none;
+  scrollbar-width: none;
+}
+.scrollbar-hide::-webkit-scrollbar {
+  display: none;
+}
+
 /* Selection color */
 ::selection {
   background: hsl(var(--primary) / 0.15);