Fix: Categories Edit IsActive checkbox now works both ways

Fixed two issues preventing IsActive toggle:
1. Removed hidden field that was sending "false" even when checkbox checked
2. Updated CategoryService to always update IsActive, treating null as false

Checkbox behavior:
- Checked → sends "true" → IsActive = true
- Unchecked → sends nothing (null) → IsActive = false (via ?? operator)

This allows both setting inactive→active and active→inactive.

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

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

LittleShop/Services/CategoryService.cs

@@ -89,10 +89,8 @@ public class CategoryService : ICategoryService
             category.Description = updateCategoryDto.Description;
         }
 
-        if (updateCategoryDto.IsActive.HasValue)
-        {
-            category.IsActive = updateCategoryDto.IsActive.Value;
-        }
+        // Always update IsActive - treat null (unchecked) as false
+        category.IsActive = updateCategoryDto.IsActive ?? false;
 
         await _context.SaveChangesAsync();
         return true;