feat: add Book type to schema and sidebar

- Add BookContentSchema with headline, subtitle, bookBody, reviewBody fields
- Add BookResource type and update GenericResourceSchema
- Add books to sidebar navigation with Bookmark Tabs icon

lib/resources.ts

@@ -24,4 +24,9 @@ export const resources = {
     name: "Series",
     link: "/series",
   },
+  "book": {
+    emoji: "Bookmark Tabs.png",
+    name: "Books",
+    link: "/books",
+  },
 } as const;