Mark items unavailable and retire DB optimization

This prepares us for the moving metadata to DB in the future

src/routes/admin.cr

@@ -1,6 +1,9 @@
 struct AdminRouter
   def initialize
     get "/admin" do |env|
+      storage = Storage.default
+      missing_count = storage.missing_titles.size +
+                      storage.missing_entries.size
       layout "admin"
     end
 
@@ -66,5 +69,9 @@ struct AdminRouter
       mangadex_base_url = Config.current.mangadex["base_url"]
       layout "download-manager"
     end
+
+    get "/admin/missing" do |env|
+      layout "missing-items"
+    end
   end
 end