Add: Replace All option to text import UI

- Add replaceAll checkbox to ImportText view with warning
- Pass replaceAll parameter to import service
- Allows complete product catalog replacement via text import
- Enhanced documentation for unit types and variant collections

LittleShop/Areas/Admin/Controllers/ProductsController.cs

@@ -252,7 +252,7 @@ public class ProductsController : Controller
 
     [HttpPost]
     [ValidateAntiForgeryToken]
-    public async Task<IActionResult> ImportText(string textContent, IFormFile? file)
+    public async Task<IActionResult> ImportText(string textContent, IFormFile? file, bool replaceAll = false)
     {
         string importText = textContent;
 
@@ -277,7 +277,7 @@ public class ProductsController : Controller
 
         try
         {
-            var result = await _importService.ImportFromHumanTextAsync(importText);
+            var result = await _importService.ImportFromHumanTextAsync(importText, replaceAll);
             ViewData["ImportResult"] = result;
             return View("ImportResult", result);
         }