Add email validation to tenant email field

Added conditional required validation and format validation for tenant email.

Changes:
- Tenant email is now required when autoTenantNotification is enabled
- Added email format validation using Zod's built-in email validator
- Email field validates format even when autoTenantNotification is off (if not empty)
- Added localization strings for validation errors (Croatian/English)

Validation logic:
- Format validation: Always checks if email is valid format (when not empty)
- Required validation: Email required when autoTenantNotification is true
- Error messages: "email address is invalid" for format, "tenant email is missing" for required

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

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

app/lib/actions/locationActions.ts

@@ -36,7 +36,7 @@ const FormSchema = (t:IntlTemplateFn) => z.object({
     tenantFirstName: z.string().optional().nullable(),
     tenantLastName: z.string().optional().nullable(),
     autoTenantNotification: z.boolean().optional().nullable(),
-    tenantEmail: z.string().optional().nullable(),
+    tenantEmail: z.string().email(t("tenant-email-invalid")).optional().or(z.literal("")).nullable(),
     addToSubsequentMonths: z.boolean().optional().nullable(),
     updateScope: z.enum(["current", "subsequent", "all"]).optional().nullable(),
   })
@@ -60,6 +60,15 @@ const FormSchema = (t:IntlTemplateFn) => z.object({
   }, {
     message: t("tenant-last-name-required"),
     path: ["tenantLastName"],
+  })
+  .refine((data) => {
+    if (data.autoTenantNotification) {
+      return !!data.tenantEmail && data.tenantEmail.trim().length > 0;
+    }
+    return true;
+  }, {
+    message: t("tenant-email-required"),
+    path: ["tenantEmail"],
   });
 
 /**