Reorgranised permission routes into their own controller

Also introduced helpers for getting entities by slugs since we do it in
so many places.

app/Entities/Models/Book.php

@@ -120,4 +120,13 @@ class Book extends Entity implements HasCoverImage
 
         return $pages->concat($chapters)->sortBy('priority')->sortByDesc('draft');
     }
+
+    /**
+     * Get a visible book by its slug.
+     * @throws \Illuminate\Database\Eloquent\ModelNotFoundException
+     */
+    public static function getBySlug(string $slug): self
+    {
+        return static::visible()->where('slug', '=', $slug)->firstOrFail();
+    }
 }

app/Entities/Models/Bookshelf.php

@@ -109,4 +109,13 @@ class Bookshelf extends Entity implements HasCoverImage
         $maxOrder = $this->books()->max('order');
         $this->books()->attach($book->id, ['order' => $maxOrder + 1]);
     }
+
+    /**
+     * Get a visible shelf by its slug.
+     * @throws \Illuminate\Database\Eloquent\ModelNotFoundException
+     */
+    public static function getBySlug(string $slug): self
+    {
+        return static::visible()->where('slug', '=', $slug)->firstOrFail();
+    }
 }

app/Entities/Models/Chapter.php

@@ -58,4 +58,13 @@ class Chapter extends BookChild
         ->orderBy('priority', 'asc')
         ->get();
     }
+
+    /**
+     * Get a visible chapter by its book and page slugs.
+     * @throws \Illuminate\Database\Eloquent\ModelNotFoundException
+     */
+    public static function getBySlugs(string $bookSlug, string $chapterSlug): self
+    {
+        return static::visible()->whereSlugs($bookSlug, $chapterSlug)->firstOrFail();
+    }
 }

app/Entities/Models/Page.php

@@ -145,4 +145,13 @@ class Page extends BookChild
 
         return $refreshed;
     }
+
+    /**
+     * Get a visible page by its book and page slugs.
+     * @throws \Illuminate\Database\Eloquent\ModelNotFoundException
+     */
+    public static function getBySlugs(string $bookSlug, string $pageSlug): self
+    {
+        return static::visible()->whereSlugs($bookSlug, $pageSlug)->firstOrFail();
+    }
 }