feat(*.php): refactor, clean up and abstract dynamic page code

api/Classes/BookFetcher.php

@@ -0,0 +1,19 @@
+<?php
+
+namespace App\Classes;
+
+class BookFetcher extends PageFetcher
+{
+  public function fetch(string $url): ?array
+  {
+    $cacheKey = "book_" . md5($url);
+    $cached = $this->cacheGet($cacheKey);
+    if ($cached) return $cached;
+
+    $book = $this->fetchSingleFromApi("optimized_books", $url);
+    if (!$book) return null;
+
+    $this->cacheSet($cacheKey, $book);
+    return $book;
+  }
+}