fix: show create user errors inside dialog, pre-fill form on error

Used novalidate + server-side validation so errors appear in the dialog
rather than as browser-native popups. Form fields retain submitted values.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/routes/admin.py

@@ -134,7 +134,6 @@ async def admin_create_user(request: Request, db: Session = Depends(get_db)):
             errors.append("Пользователь с таким email уже существует")
 
     if errors:
-        # Re-render list page with errors and dialog open
         q = db.query(User)
         total = q.count()
         users = q.order_by(User.created_at.desc()).limit(PAGE_SIZE).all()
@@ -148,6 +147,13 @@ async def admin_create_user(request: Request, db: Session = Depends(get_db)):
             "total_pages": max(1, (total + PAGE_SIZE - 1) // PAGE_SIZE),
             "total": total,
             "create_errors": errors,
+            "create_form": {
+                "first_name": first_name,
+                "last_name": last_name,
+                "email": email,
+                "phone": phone or "",
+                "role": role_str,
+            },
         })
 
     try: