add chapter about data repositories, and start work on perfomance chapter

app/src/Model/MarkdownPage.php

@@ -2,19 +2,11 @@
 
 namespace Lubian\NoFramework\Model;
 
-use Doctrine\DBAL\Types\Types;
-
-#[Entity]
 class MarkdownPage
 {
     public function __construct(
-        #[Id,
-        Column,
-        GeneratedValue]
         public int |null $id = null,
-        #[Column]
         public string $title,
-        #[Column(type: Types::TEXT)]
         public string $content,
     ) {
     }