fix: prevent double form submission in employee edit form

Problem:
- When editing employee profile, got duplicate PATCH requests
- One request returned 502, another 200 OK
- Error appeared in console but operation succeeded
- Classic double-submit race condition

Root Cause:
initEmployeeForm() added new addEventListener('submit') on every call.
If function was called twice (e.g., on tab navigation or re-render),
two event handlers would fire simultaneously, sending parallel requests.

Solution:
1. Check if form already initialized via data-attribute
2. Set form.dataset.employeeFormInitialized = 'true' flag
3. Skip re-initialization if already initialized
4. Return API object for already initialized forms

This ensures only ONE submit handler per form, preventing:
- Duplicate PATCH requests
- 502 errors from race conditions
- Confusing UX with errors that don't break functionality

Now form submits cleanly with single request.

backend/static/js/components/employeeFormHandler.js

@@ -12,7 +12,22 @@ export function initEmployeeForm(options = {}) {
     return null;
   }
 
+  // Проверяем, не была ли форма уже инициализирована
+  if (form.dataset.employeeFormInitialized === 'true') {
+    console.warn('[EmployeeForm] Форма уже инициализирована, пропускаем повторную инициализацию');
+    return {
+      setSubmitting: (state) => {
+        const submitBtn = form.querySelector('button[type="submit"]');
+        if (submitBtn) submitBtn.disabled = state;
+      },
+      refresh: () => location.reload()
+    };
+  }
+
   console.info('[EmployeeForm] Инициализация AJAX обработчика формы');
+  
+  // Помечаем форму как инициализированную
+  form.dataset.employeeFormInitialized = 'true';
 
   // Перехватываем submit формы
   form.addEventListener('submit', async (e) => {