feat: add user locale preference to user_preferences table (#555)

* feat: add user locale preference to user_preferences table

- Introduced a new column 'locale' in the user_preferences table to store per-user UI language preferences.
- Added a CHECK constraint to ensure only supported locales ('sv', 'en') are allowed.
- Triggered a schema reload notification for the changes.

chore: declare CSS module support in TypeScript

- Added a declaration for CSS modules in globals.d.ts to enable TypeScript support for importing CSS files.

* feat: add Swish as an invoice payment method in company settings

lib/utils.ts

@@ -25,12 +25,17 @@ export function formatDate(date: Date | string): string {
 }
 
 /**
- * Long-form Swedish date for metadata/audit contexts (e.g. "9 maj 2026").
+ * Long-form date for metadata/audit contexts (e.g. "9 maj 2026" / "May 9, 2026").
  * Use formatDate for transaction/voucher/invoice dates that need to align in tables.
+ *
+ * The locale arg is the UI language ('sv' | 'en'); default 'sv' keeps existing
+ * server-side callers (logs, audit) Swedish without churn. For client UI use
+ * the useFormat() hook which pulls the active locale from next-intl.
  */
-export function formatDateLong(date: Date | string): string {
+export function formatDateLong(date: Date | string, locale: string = 'sv'): string {
   const d = typeof date === 'string' ? parseISO(date) : date
-  return d.toLocaleDateString('sv-SE', {
+  const intlLocale = locale === 'en' ? 'en-US' : 'sv-SE'
+  return d.toLocaleDateString(intlLocale, {
     day: 'numeric',
     month: 'short',
     year: 'numeric',