Add tenant information fields to LocationEditForm

Added optional tenant fields (first name, last name, email) to billing locations
with a toggle to enable/disable 2D barcode generation for tenants.

Changes:
- Added generateTenantCode, tenantFirstName, tenantLastName, and tenantEmail
  fields to BillingLocation interface
- Updated LocationEditForm with toggle control and conditional tenant fields
- Implemented conditional validation: tenant names required when generateTenantCode is true
- Updated updateOrAddLocation action to persist tenant data across all update operations
- Added localization strings for tenant fields and validation messages (Croatian/English)

The generateTenantCode flag is persisted in the database and controls visibility
of tenant name fields. When enabled, both first and last names become mandatory.

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

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

messages/en.json

@@ -124,6 +124,14 @@
   "location-edit-form": {
     "location-name-placeholder": "Realestate name",
     "notes-placeholder": "Notes",
+    "generate-tenant-code": "Generate 2D code for tenant",
+    "tenant-first-name-label": "Tenant First Name",
+    "tenant-first-name-placeholder": "Enter tenant's first name",
+    "tenant-last-name-label": "Tenant Last Name",
+    "tenant-last-name-placeholder": "Enter tenant's last name",
+    "tenant-email-label": "Tenant Email",
+    "tenant-email-placeholder": "Enter tenant's email",
+    "warning-missing-tenant-names": "Warning: Tenant first and last name are missing. The 2D barcode will not be displayed to the tenant when they open the shared link until both fields are filled in.",
     "save-button": "Save",
     "cancel-button": "Cancel",
     "delete-tooltip": "Delete realestate",
@@ -133,7 +141,10 @@
     "update-subsequent-months": "current and all future months",
     "update-all-months": "all months",
     "validation": {
-      "location-name-required": "Relaestate name is required"
+      "location-name-required": "Relaestate name is required",
+      "tenant-first-name-required": "tenant first name is missing",
+      "tenant-last-name-required": "tenant last name is missing",
+      "validation-failed": "Validation failed. Please check the form and try again."
     }
   },
   "account-form": {