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>

app/lib/db-types.ts

@@ -43,6 +43,14 @@ export interface BillingLocation {
     bills: Bill[];
     /** (optional) notes */
     notes: string|null;
+    /** (optional) whether to generate 2D code for tenant */
+    generateTenantCode?: boolean | null;
+    /** (optional) tenant first name */
+    tenantFirstName?: string | null;
+    /** (optional) tenant last name */
+    tenantLastName?: string | null;
+    /** (optional) tenant email */
+    tenantEmail?: string | null;
 };
 
 export enum BilledTo {