Move currency selector to separate General Settings section

Changes:
- Reorganized UserSettingsForm layout
- Moved currency select field from tenant 2D code fieldset
  to new "General Settings" fieldset at the top of the form
- Added translations for "general-settings-legend":
  - English: "General Settings"
  - Croatian: "Opće postavke"

Currency is now in a more logical location as a general setting
rather than being grouped with tenant-specific 2D code settings.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

messages/en.json

@@ -197,6 +197,7 @@
     "owner-town-placeholder": "enter your postal code and town",
     "owner-iban-label": "IBAN",
     "owner-iban-placeholder": "enter your IBAN",
+    "general-settings-legend": "General Settings",
     "currency-label": "Currency",
     "save-button": "Save",
     "cancel-button": "Cancel",